Use GitHub Actions to build documentation

[bquorning]

Pulling repositories and building documentation takes 10–13 minutes on my very fast laptop, and I don’t know if there’s any way to speed it up. So I was thinking if we could at least move the work to GitHub Actions, meaning that I would only need to update the playbook file and then GHA would do the actual work – is that possible?

[bquorning]

cc @bbatsov

[bbatsov]

Yeah, it's possible, I just never got to doing it - https://docs.antora.org/antora/latest/publish-to-github-pages/#using-github-actions