Add docs for the carvel plugin

[antgamdia]

Description of the change

This PR brings a new docs item covering how to use the carvel kapp-controller plugin in Kubeapps.

Benefits

The plugin will get finally documented :P

Possible drawbacks

N/A

Applicable issues

• fixes Document the current support for the Carvel plugin #4092

Additional information

In progress, I've sent the PR if someone is interested in having a look at the current progress.

[castelblanque]

Superb! Really nice and comprehensive guide to the Carvel in Kubeapps.
Just for being picky: in the package repository section we show a simple repository CR, shouldn't we mention which features Kubeapps is able to use? e.g. authentication for repos, etc.

[antgamdia]

the package repository section we show a simple repository CR, shouldn't we mention which features Kubeapps is able to use? e.g. authentication for repos, etc.

Mmm, currently I haven't explored authenticated repos in kapp-controller. I'm aware there is a secretgen-controller, but you can manually create the repo adding a secretRef like:

  fetch:
    imgpkgBundle:
      image: k8slt/corp-com-pkg-repo:1.0.0
      secretRef:
        name: my-registry-creds

(reference: https://carvel.dev/kapp-controller/docs/latest/private-registry-auth/#manual-configuration-without-secretgen-controller)

However, since regardless of the cool features it has, Kubeapps will never show any Carvel repo in the UI as long as the repository API is not refactored. That's why I just try to keep it simple, we will have to re-word the whole section in the near future.

Anyway, happy to add more details if you think so.