Update docs to use Helm chart from OCI registry (#3565)

**What this PR does / why we need it**:

**Which issue(s) this PR fixes**:

Fixes #

**Does this PR introduce a user-facing change?**:
<!--
If no, just write "NONE" in the release-note block below.
-->
```release-note
NONE
```

This PR was merged by Kapetanios.

docs/content/en/docs-dev/operator-manual/control-plane/installation.md

@@ -9,21 +9,11 @@ description: >
 ## Prerequisites
 
 - Having a running Kubernetes cluster
-- Installed [helm3](https://helm.sh/docs/intro/install/)
+- Installed [Helm](https://helm.sh/docs/intro/install/) (3.8.0 or later)
 
 ## Installation
 
-### 1. Adding helm chart repository
-
-Installing the control-plane will be done via the helm chart sourced in [pipe-cd/manifests](https://github.com/pipe-cd/manifests/tree/master/manifests/pipecd) GitHub repository. That chart is published in the Helm chart repository at `https://charts.pipecd.dev`.
-
-So before installing PipeCD, let's add the above Helm chart repository to your Helm client by the following command:
-
-``` console
-helm repo add pipecd https://charts.pipecd.dev
-```
-
-### 2. Preparing an encryption key
+### 1. Preparing an encryption key
 
 PipeCD requires a key for encrypting sensitive data or signing JWT token while authenticating. You can use one of the following commands to generate an encryption key.
 
@@ -34,7 +24,7 @@ openssl rand 64 | base64 > encryption-key
 cat /dev/urandom | head -c64 | base64 > encryption-key
 ```
 
-### 3. Preparing control-plane configuration file and installing
+### 2. Preparing control-plane configuration file and installing
 
 As described at the [architecture overview](/docs/operator-manual/control-plane/architecture-overview/) page, the control-plane's data can be stored in one of the provided fully-managed or self-managed services. So you have to decide which kind of [data store](/docs/operator-manual/control-plane/architecture-overview/#data-store) and [file store](/docs/operator-manual/control-plane/architecture-overview/#file-store) you want to use and prepare a control-plane configuration file suitable for that choice.
 
@@ -70,7 +60,7 @@ See [ConfigurationReference](/docs/operator-manual/control-plane/configuration-r
 After all, install the control-plane as bellow:
 
 ``` console
-helm install pipecd pipecd/pipecd --version={{< blocks/latest_version >}} --namespace={NAMESPACE} \
+helm install pipecd oci://ghcr.io/pipe-cd/chart/pipecd --version {{< blocks/latest_version >}} --namespace={NAMESPACE} \
   --set-file config.data=path-to-control-plane-configuration-file \
   --set-file secret.encryptionKey.data=path-to-encryption-key-file \
   --set-file secret.firestoreServiceAccount.data=path-to-service-account-file \

docs/content/en/docs-dev/operator-manual/piped/installation/installing-on-kubernetes.md

@@ -19,13 +19,6 @@ description: >
 ## In the cluster-wide mode
 This way requires installing cluster-level resources. Piped installed with this way can perform deployment workloads against any other namespaces than the where Piped runs on.
 
-- Adding `pipecd` helm chart repository
-
-  ```
-  helm repo add pipecd https://charts.pipecd.dev
-  helm repo update
-  ```
-
 - Preparing a piped configuration file as the following
 
   ``` yaml
@@ -46,15 +39,15 @@ This way requires installing cluster-level resources. Piped installed with this
     syncInterval: 1m
   ```
 
-- Installing by using `Helm 3`
+- Installing by using [Helm](https://helm.sh/docs/intro/install/) (3.8.0 or later)
 
   {{< tabpane >}}
   {{< tab lang="bash" header="Piped" >}}
 # This command just installs a Piped with the specified version.
 # Whenever you want to upgrade that Piped to a new version or update its config data
 # you have to restart it by re-running this command.
 
-helm upgrade -i dev-piped pipecd/piped --version={{< blocks/latest_version >}} --namespace={NAMESPACE} \
+helm upgrade -i dev-piped oci://ghcr.io/pipe-cd/chart/piped --version={{< blocks/latest_version >}} --namespace={NAMESPACE} \
   --set-file config.data={PATH_TO_PIPED_CONFIG_FILE} \
   --set-file secret.data.piped-key={PATH_TO_PIPED_KEY_FILE} \
   --set-file secret.data.ssh-key={PATH_TO_PRIVATE_SSH_KEY_FILE}
@@ -65,7 +58,7 @@ helm upgrade -i dev-piped pipecd/piped --version={{< blocks/latest_version >}} -
 # This allows upgrading Piped to a new version from the web console.
 # But we still need to restart Piped when we want to update its config data.
 
-helm upgrade -i dev-piped pipecd/piped --version={{< blocks/latest_version >}} --namespace={NAMESPACE} \
+helm upgrade -i dev-piped oci://ghcr.io/pipe-cd/chart/piped --version={{< blocks/latest_version >}} --namespace={NAMESPACE} \
   --set launcher.enabled=true \
   --set-file config.data={PATH_TO_PIPED_CONFIG_FILE} \
   --set-file secret.data.piped-key={PATH_TO_PIPED_KEY_FILE} \
@@ -78,7 +71,7 @@ helm upgrade -i dev-piped pipecd/piped --version={{< blocks/latest_version >}} -
 # remote-config allows loading the Piped config stored in a remote location such as a Git repository.
 # Whenever the config data is changed, it loads the new config and restarts Piped to use that new config.
 
-helm upgrade -i dev-piped pipecd/piped --version={{< blocks/latest_version >}} --namespace={NAMESPACE} \
+helm upgrade -i dev-piped oci://ghcr.io/pipe-cd/chart/piped --version={{< blocks/latest_version >}} --namespace={NAMESPACE} \
   --set launcher.enabled=true \
   --set launcher.configFromGitRepo.enabled=true \
   --set [email protected]:{GIT_ORG}/{GIT_REPO}.git \
@@ -125,15 +118,15 @@ Most parts are identical to the previous way, but some are slightly different.
             namespace: {NAMESPACE}
   ```
 
-- Installing by using `Helm 3`
+- Installing by using [Helm](https://helm.sh/docs/intro/install/) (3.8.0 or later)
 
   {{< tabpane >}}
   {{< tab lang="bash" header="Piped" >}}
 # This command just installs a Piped with the specified version.
 # Whenever you want to upgrade that Piped to a new version or update its config data
 # you have to restart it by re-running this command.
 
-helm upgrade -i dev-piped pipecd/piped --version={{< blocks/latest_version >}} --namespace={NAMESPACE} \
+helm upgrade -i dev-piped oci://ghcr.io/pipe-cd/chart/piped --version={{< blocks/latest_version >}} --namespace={NAMESPACE} \
   --set-file config.data={PATH_TO_PIPED_CONFIG_FILE} \
   --set-file secret.data.piped-key={PATH_TO_PIPED_KEY_FILE} \
   --set-file secret.data.ssh-key={PATH_TO_PRIVATE_SSH_KEY_FILE} \
@@ -146,7 +139,7 @@ helm upgrade -i dev-piped pipecd/piped --version={{< blocks/latest_version >}} -
 # This allows upgrading Piped to a new version from the web console.
 # But we still need to restart Piped when we want to update its config data.
 
-helm upgrade -i dev-piped pipecd/piped --version={{< blocks/latest_version >}} --namespace={NAMESPACE} \
+helm upgrade -i dev-piped oci://ghcr.io/pipe-cd/chart/piped --version={{< blocks/latest_version >}} --namespace={NAMESPACE} \
   --set launcher.enabled=true \
   --set-file config.data={PATH_TO_PIPED_CONFIG_FILE} \
   --set-file secret.data.piped-key={PATH_TO_PIPED_KEY_FILE} \
@@ -161,7 +154,7 @@ helm upgrade -i dev-piped pipecd/piped --version={{< blocks/latest_version >}} -
 # remote-config allows loading the Piped config stored in a remote location such as a Git repository.
 # Whenever the config data is changed, it loads the new config and restarts Piped to use that new config.
 
-helm upgrade -i dev-piped pipecd/piped --version={{< blocks/latest_version >}} --namespace={NAMESPACE} \
+helm upgrade -i dev-piped oci://ghcr.io/pipe-cd/chart/piped --version={{< blocks/latest_version >}} --namespace={NAMESPACE} \
   --set launcher.enabled=true \
   --set launcher.configFromGitRepo.enabled=true \
   --set [email protected]:{GIT_ORG}/{GIT_REPO}.git \
@@ -182,15 +175,15 @@ Starting from OpenShift 4.2, it also inserts that user into `/etc/passwd` for us
 but before that version, the assigned user is missing in that file. That blocks workloads of `gcr.io/pipecd/piped` image.
 Therefore if you are running on OpenShift with a version before 4.2, please use `gcr.io/pipecd/piped-okd` image with the following command:
 
-- Installing by using `Helm 3`
+- Installing by using [Helm](https://helm.sh/docs/intro/install/) (3.8.0 or later)
 
   {{< tabpane >}}
   {{< tab lang="bash" header="Piped" >}}
 # This command just installs a Piped with the specified version.
 # Whenever you want to upgrade that Piped to a new version or update its config data
 # you have to restart it by re-running this command.
 
-helm upgrade -i dev-piped pipecd/piped --version={{< blocks/latest_version >}} --namespace={NAMESPACE} \
+helm upgrade -i dev-piped oci://ghcr.io/pipe-cd/chart/piped --version={{< blocks/latest_version >}} --namespace={NAMESPACE} \
   --set-file config.data={PATH_TO_PIPED_CONFIG_FILE} \
   --set-file secret.data.piped-key={PATH_TO_PIPED_KEY_FILE} \
   --set-file secret.data.ssh-key={PATH_TO_PRIVATE_SSH_KEY_FILE} \
@@ -209,7 +202,7 @@ helm upgrade -i dev-piped pipecd/piped --version={{< blocks/latest_version >}} -
 # This allows upgrading Piped to a new version from the web console.
 # But we still need to restart Piped when we want to update its config data.
 
-helm upgrade -i dev-piped pipecd/piped --version={{< blocks/latest_version >}} --namespace={NAMESPACE} \
+helm upgrade -i dev-piped oci://ghcr.io/pipe-cd/chart/piped --version={{< blocks/latest_version >}} --namespace={NAMESPACE} \
   --set launcher.enabled=true \
   --set-file config.data={PATH_TO_PIPED_CONFIG_FILE} \
   --set-file secret.data.piped-key={PATH_TO_PIPED_KEY_FILE} \
@@ -230,7 +223,7 @@ helm upgrade -i dev-piped pipecd/piped --version={{< blocks/latest_version >}} -
 # remote-config allows loading the Piped config stored in a remote location such as a Git repository.
 # Whenever the config data is changed, it loads the new config and restarts Piped to use that new config.
 
-helm upgrade -i dev-piped pipecd/piped --version={{< blocks/latest_version >}} --namespace={NAMESPACE} \
+helm upgrade -i dev-piped oci://ghcr.io/pipe-cd/chart/piped --version={{< blocks/latest_version >}} --namespace={NAMESPACE} \
   --set launcher.enabled=true \
   --set launcher.configFromGitRepo.enabled=true \
   --set [email protected]:{GIT_ORG}/{GIT_REPO}.git \

docs/content/en/docs-dev/quickstart/_index.md

@@ -12,17 +12,14 @@ Note: It's not required to install the PipeCD control plane to the cluster where
 
 ### Prerequisites
 - Having a Kubernetes cluster
-- Installed [kubectl](https://kubernetes.io/docs/tasks/tools/install-kubectl/) and [helm3](https://helm.sh/docs/intro/install/)
+- Installed [kubectl](https://kubernetes.io/docs/tasks/tools/install-kubectl/) and [Helm](https://helm.sh/docs/intro/install/) (3.8.0 or later)
 - Forked the [Examples](https://github.com/pipe-cd/examples) repository
 
 ### 1. Installing control plane
 
 ``` console
-helm repo add pipecd https://charts.pipecd.dev
-
-helm install pipecd pipecd/pipecd -n pipecd \
-  --create-namespace \
-  --dependency-update \
+helm install pipecd oci://ghcr.io/pipe-cd/chart/pipecd --version {{< blocks/latest_version >}} \
+  --namespace pipecd --create-namespace \
   --values https://raw.githubusercontent.com/pipe-cd/manifests/{{< blocks/latest_version >}}/quickstart/control-plane-values.yaml
 ```
 
@@ -54,7 +51,8 @@ Be sure to keep a copy for later use.
 Then complete the installation by running the following command after replacing `{PIPED_ID}`, `{PIPED_KEY}`, `{FORKED_GITHUB_ORG}` with what you just got:
 
 ``` console
-helm install piped pipecd/piped -n pipecd \
+helm install piped oci://ghcr.io/pipe-cd/chart/piped --version {{< blocks/latest_version >}} \
+  --namespace pipecd \
   --set quickstart.enabled=true \
   --set quickstart.pipedId={PIPED_ID} \
   --set secret.data.piped-key={PIPED_KEY} \