pre-commit hook break git commits and are disruptive.
Therefore people that want to enable this feature, should enable it locally instead.
I.e. treefmt will also check untracked files that are not meant for the current commit.
make sure things are sane before they hit CI, re-purposing the existing
treefmt configuration.
this adds a custom installer for pre-commit hooks, which is inspired by
pre-commit.nix[0], but is much more minimal than the underlying
pre-commit[1] and builds on a historic idea[2] from this repository.
[0]: https://github.com/cachix/git-hooks.nix
[1]: https://github.com/pre-commit/pre-commit
[2]: 930923512c