Since there's no auto deletion of merged branches, auto-rebase branches are being accumulated: https://github.com/openshift/microshift/branches

Goal is to add cleanup in create-pr.py that would (using GitHub API; or rather pygithub) list remote branches, take those named `^rebase-*`, get a PR for each - if the PR is closed (or merged), then delete the branch on the remote.

https://docs.github.com/en/rest/pulls/pulls#list-pull-requests

https://docs.github.com/en/rest/branches/branches#list-branches

https://docs.github.com/en/rest/git/refs#delete-a-reference