[all] Common structure for Greenhouse Plugins

[IvoGoman]

Priority

(Medium) I'm annoyed but I'll live

Is your feature request related to a problem?

Currently there is no common file structure for Plugins, which requires manually adding each new plugin into the ct.yaml and now also for running the Helm Chart Tests during PRs.
Also there are Dockerfiles for Plugins in the root of the repository, which all need to be registered in the GH actions manually.

This potentially requires touching 3 files when creating a new plugin, which is partially due to having different folder structures and names for different plugins.

Ideally, there is a common file structure for all plugins. Maybe something like:

my-plugin:
  chart:
    templates:
      tests:
    Chart.yaml
  dockerfiles:
    Dockerfile.<image-name>

Which could help automate the CI to run the lint on the chart contained in my-plugin/chart/**
Which could help automate the CI to way run chart tests if the Plugin changed in the PR contains a chart/template/tests folder.
Which could auto-discover all Dockerfiles.<image-name> and build them.

Additional context.

No response

Reference Issues

#389