ci: Add some automation for making releases

[paulgessinger]

With this PR, there's one action that runs on any PR that targets branches releases or release/*, and will make a trial run of the changelog generation and version bumping. This only works on PRs on the main repo, for permission reasons.

A second action will automatically run on branches releases or release/*, generate the changelog, execute the version bump, and finally create a GitHub release with the generated changelog and version number. This release can be manually published, and when that happens, a git tag is created on the bump commit.

I've tested all this over on https://github.com/paulgessinger/release-test but I don't think it's bulletproof. I'd like to run this for a bit and see if it does the job. There is the possibility for manual intervention before anything (kind of) irreversible happens, so that should be fine.

[codecov]

Codecov Report

Merging #969 (95440ed) into main (8236d1f) will not change coverage.
The diff coverage is n/a.

❗ Current head 95440ed differs from pull request most recent head fc99d2b. Consider uploading reports for the commit fc99d2b to get more accurate results

@@           Coverage Diff           @@
##             main     #969   +/-   ##
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  Coverage   48.48%   48.48%           
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  Files         334      334           
  Lines       17091    17091           
  Branches     8081     8081           
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  Hits         8287     8287           
  Misses       3099     3099           
  Partials     5705     5705           

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[HadrienG2]

My python is too rusty to make sense of everything, but looks reasonable from a general look around.