Stop image push for quay.io

[ccremer]

Summary

• Having everything at GitHub should be fine enough, no need to maintain 2 registries.
• Existing tags and images on quay.io will remain for the time being.
• New images and releases will be pushed to ghcr.io only.

Marked as "breaking" since users would potentially need to switch the registry in their configuration. Nothing has changed in behaviour (code).

Checklist

For Code changes

• Categorize the PR by setting a good title and adding one of the labels:
  kind:bug, kind:enhancement, kind:documentation, kind:change, kind:breaking, kind:dependency
  as they show up in the changelog
• PR contains the label area:provisioner
• I have not made any changes in the charts/ directory.