Automate moving of the stable branches

[lachmanfrantisek]

We'd like to automate moving the stable branches and creating a blog post so that the scripts don't need to be run locally.

Definition of done:

• moving of the stable branches and creation of the weekly packit.dev blog posts are run in a Github action
  • the work that is currently done by running a script locally will be moved to a GitHub action that can be triggered manually in Github UI (=> the script can run non-interactively)
  • the PR with the blog post will be opened automatically by running the action and the content can be modified by a person
• instructions for the Service Guru role are updated

When this is done, our team will benefit from elimination of human errors during the process.

[lachmanfrantisek]

After a team discussion, we didn't pick this as a top Packit team priority for the next quarter and preferred epics with bigger user benefits. (Sadly, we have limited resources...)