Adding etcdctl and k9s install on demand script to make usage easier

[mimiteto]

What this PR does / why we need it:
This PR should make a bit easier for persons who troubleshoot to install etcdctl.

Which issue(s) this PR fixes:
Fixes #

Special notes for your reviewer:
I mostly copied/adapted things based on the existing install script and the same script for wireguard.
To check if the modification works as expected I did a local build of the image and tried installing and using etdctl.

Release note:

`etcdctl` command is now available within the `ops-toolbelt` image. Upon first invocation it will be installed and will be fully usable.
`etcdctl` is also trying to guess the parameter values for connectivity to the `etcd` instance.

`k9s` command is now available within the `ops-toolbelt` image. Upon first invocation it will be installed and will be fully usable.

On demand installations now work with any user within the image.

[petersutter]

Why don't we just install the latest version instead of asking the user?

[mimiteto]

I just took two current scripts - dotfiles/.install_on_demand/.wireguard and hacks/install_etcdctl.
In the hacks script there is an option for the version, that's why it's transformed to a question (that's how it's handled in the other scripts).
Just a note, after discussing with @plkokanov - current PR will not be actually that useful.
If you decide to use the ops-toolbelt with non-root user you actually don't have access to dotfiles, so additional change is needed (for example, loading dotfiles in /etc/bashrc).
I still haven't gotten around to check this approach.

[petersutter]

In the hacks script there is an option for the version, that's why it's transformed to a question (that's how it's handled in the other scripts).

I think we should just install the latest version, if the user runs etcdctl or wg. If they want to have a specific version, they should run the install script and pass the version as argument

[petersutter]

btw. I have also created #104 for k9s as we have an install script for this as well but does not yet support to install it on demand

[mimiteto]

If they want to have a specific version, they should run the install script and pass the version as argument

Arguments are passed directly to the binaries after they are installed, so I am not sure if that's a good idea.

IMO having the option to specify version can come in handy and first invocation of those commands will anyway break whatever script (because of the y/n part) so I don't see a reason to currently remove versions.

It would make sense if we decide to change it so when an operator invokes, for example, wg if it's not installed to automatically install, no questions asked. In that case I agree having the option to specify a version is pointless.

[petersutter]

What about the following:

• The install script should not invoke the binary. It should just install it. If you pass a version as argument it should take it, otherwise it should install the latest (or maybe a hardcoded version, depends on how we want it to behave).
• Running the binary, like etcdctl should install it on demand in case it is not already installed, no questions asked to the user. We could redirect any output of the install script to stderr, which could make it more compatible with scripts calling it for the first time..

[mimiteto]

I made the on-demand binaries get installed when executed without any questions asked.
I also changed the etcdctl install script to consider current user (root goes to the system path, non-root uses dir relevant to the current user).
In addition I made the etcdctl alias add arguments about certificates in the default paths when etcdctl is executed within debug pod.
PR is currently incomplete, as it still needs to change the way dotfiles are made available

[petersutter]

PR is currently incomplete

do you want to change it to draft then?

[mimiteto]

After a sync with @petersutter:

• I've reverted the ops-pod script
• I've dropped the image pull policy - that way we will default to Always if no image is specified, because default image in the script has latest tag. Otherwise we will default to the IfNotPresent

[petersutter]

/lgtm

[plkokanov]

Just a few more minor suggestions. Rest looks very good, I think.

[plkokanov]

/lgtm