[llvm] workflows: Add some automation for commit access requests (PR #123113)

[Aiden Grossman via llvm-commits]

https://github.com/boomanaiden154 approved this pull request.

Minor style nits, otherwise LGTM.

I thank at some point it might be good to split `github-automation.py`, but this seems to work reasonably enough for now.

https://github.com/llvm/llvm-project/pull/123113