Update go-yaml with changes to indentation style

[stefanprodan]

This PR updates the YAML packages (used by the controller to patch Kubernetes manifests) to fix long standing issues like panics that make the controller unusable for many users.

Dependencies changes:

• update gopkg.in/yaml.v3 from v3.0.0-20200313102051-9f266ea9e77c to v3.0.0-20200615113413-eeeca48fe776 (fix: controller crash when patching YAMLs with non-ASCII characters #140)
• update sigs.k8s.io/kustomize/kyaml from v0.10.19 to v0.10.21

Breaking change

The gopkg.in/yaml.v3 update means that the indentation style changed:

From:

spec:
  containers:
  - name: one
    image: image1:v1.0.0 # {"$imagepolicy": "automation-ns:policy1"}
  - name: two
    image: image2:v1.0.0 # {"$imagepolicy": "automation-ns:policy2"}

To:

spec:
  containers:
    - name: one
      image: image1:v1.0.0 # {"$imagepolicy": "automation-ns:policy1"}
    - name: two
      image: image2:v1.0.0 # {"$imagepolicy": "automation-ns:policy2"}

While Kustomize kyaml is using an older version of go-yaml we can't hold onto this forever. I find it unacceptable for Flux to keep crashing due to bugs fixed upstream in go-yaml. Kustomize may chose to delay this update (see kubernetes-sigs/kustomize#3789 and kubernetes-sigs/kustomize#3946) but this doesn't mean we are obliged to do the same. The image automation is alpha and breaking changes like this are acceptable considering the tradeoffs. I hope at some point, go-yaml will be able to detect and preserve the original indentation but it seems unlikely go-yaml/yaml#661 (comment)

Closes #92

[hiddeco]

While Kustomize kyaml is using an older version of go-yaml we can't hold onto this forever. I find it unacceptable for Flux to keep crashing due to bugs fixed upstream in go-yaml.

I do agree, and think that the number of issues it resolves outweigh the breaking change introduces.

👍 from me.

[squaremo]

Meta-approval (I trust the other reviewer(s)): I am fine with the breaking change, so long as we flag it prominently, of course.