Add Nix to pre-commit

Add Nix as language to pre-commit. In the end, any-body should be able to create a new hook as a nix-flakes entry point. It would be cool if regular nix package could be used too.

DifficultyLow
Project URLhttps://github.com/pre-commit/pre-commit
Programming languagepython
Project typeOpen source contribution

How To Do it.

Basically, we need to add two different languages to the all_languages.py, one for nix-pkgs, one for nix-flakes. The language should be super simple, just run the specific target with the appropriate commands. The simplest language is the system language but a good example of a more complex language is the python language.