Support vendir's githubRelease

[jorgemoralespou]

Describe the problem/challenge you have
vendir does support githubRelease to fetch artifacts

Describe the solution you'd like
kapp-controller support for same feature as vendir to fetch githubRelease

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[100mik]

Could you elaborate on your exact use case?
Without context however, it feels like it would be recommended to wrap a release into a Package in most cases 🤔

Some context would also help us figure out if there are other folks who are looking for something like this as well.

[jorgemoralespou]

I'm trying to migrate vendir's/ytt/kbld/kapp done out of cluster into a kapp-controller's App to run it within cluster. I'm currently using vendir's githubRelease to fetch release artifacts, and if I need to use git instead I need to alter how I produce artifacts in the source repository as the release files are not available in the git repository as it is. It'll be ideal to fully support vendir's capabilities so that it's easy to move imperative provisioning to declarative in cluster GitOps like via Apps.