[llvm] [Utils] Add new merge-release-pr.py script. (PR #101630)

[Aiden Grossman via llvm-commits]

https://github.com/boomanaiden154 commented:

Main comment is about using docstrings over just comments about the function (https://google.github.io/styleguide/pyguide.html#38-comments-and-docstrings). We don't have an official Python style guide (maybe we should start one), but I think it's a reasonable enough format and standardized enough, at least in the code that I read (which is a _bit_ biased towards one style).

We could also use the Github API here to grab the PR info/do stuff, but using the `gh` tool seems good enough, and if that's what the release managers have setup, then that's what we should go with because they're the ones ultimately using it.

Writing tests looks like it would mostly be integration tests while mocking the Github API/CLI tool, which would be a massive pain for not much benefit.

https://github.com/llvm/llvm-project/pull/101630