Use gh CLI to automatically set up repo protection rules and settings

[Marenz]

When initializing a new repository, it would be useful to automatically configure branch protection rules, required status checks, and other repository settings using the gh CLI (or GitHub API via gh api).

This could be part of the repo setup tooling so new repos don't require manual configuration steps in the GitHub UI.

Things to consider:

• Branch protection rules (require PR reviews, status checks, signed commits, etc.)
• Default branch settings
• Repository features (issues, wiki, projects)
• Potentially as a frequenz-repo-config command or nox session

[llucax]

Yeah, I had it at the back of my mind for a while now. I thought there was an issue for it, but maybe I'm remembering wrong and we only have this one:

• Create a repo-config CLI tool #158

So I was thinking about some sort of repo-config new that just calls cookiecutter and then continue with the setup via API. And repo-config update that would run the migration.

I think that approach would be nice, but sort of a high-hanging fruit, so going for something simpler, like we did with cookiecutter/migrate.py might be more realistic.

[llucax]

A create new repo command could even create the GitHub repo for you.