Summary

Update Antora boilerplate and GH action so that the documentation gets published in this repo (instead of https://github.com/ccremer/clustercode-docs)

as a consequence, the old docs will not be updated anymore, and may later go archived completely: https://ccremer.github.io/clustercode-docs

Checklist

• 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:operator
• Link this PR to related issues
• I have not made any changes in the charts/ directory.