Using pre-commit hooks

[knoepfel]

We use a variety of formatting tools for the code in the phlex repository, which is written in C++, Python, YAML, CMake, Jsonnet, etc. Although there is a comment-based GitHub action that can apply formatting conventions to the pull request, we should consider incorporating https://pre-commit.com into our development workflow.

[olantwin]

We've made very positive experiences with pre-commit in SHiP, both for C++ and Python code.

I can prepare a PR with the first few hooks (e.g. clang-format, yaml syntax checking, ruff format, file endings, trailing whitespace) tomorrow.
I also saw that there's a hook for jsonnetfmt, but it seems unmaintained.

Would you also be interested in using the CI service? It's free for public github projects and very convenient.