Feature Request: check-mailmap alphabetize

I am a fan of `check-mailmap` and use this hook.

I think it would be cool if `check-mailmap` had an argument to confirm the `.mailmap` is alphabetically ordered.

Bonus points: in-place modify the `.mailmap` to be alphabetic, similar to how an autoformatter pre-commit hook (e.g. `black`, `isort`) would do.