Always create stable branches?

This is prompted by !418 (closed).

Maybe stable branches should always get created when master opens up for new development after a release?

Otherwise people cannot cherry-pick patches and submit MRs for stable branches, which means we basically stop any stable branch maintenance from ever occurring.

If people were able to submit MRs against stable branches, reviewing those MRs should be a breeze most of the time (Did it use git cherry-pick -x? Is it only a bug fix?). If contributors help pick the patches for stable branches, maybe the release manager doesn't need to do anything more than cut releases sometimes.