Configure automatically generated release notes

This issue is of **very low** importance, but we could generate more stratified release notes if we wanted to according to the PR labels.
By configuring some YAML file somewhere in the repository, we could say that, for example, everything with the `area:llvm` label is then in a special "LLVM" section. This could then help to produce easy-to-skim release notes.

See docs for more details: https://docs.github.com/en/repositories/releasing-projects-on-github/automatically-generated-release-notes#configuring-automatically-generated-release-notes

Testing this is a bit cumbersome, probably easier by making a fork of the repo and letting the `autorelease.yml` action run every day / running it manually.

Follow-up from #538.