Support post-checkout

[domenkozar]

I know this goes beyond the original intention (and the name), but it would be really useful to be able to use same pre-commit hooks for different git hooks.

We need to run some validation before checking out. The alternative is to use https://github.com/sds/overcommit, but I'd prefer for pre-commit to get better.

[asottile]

sure! there's already a few other git hooks supported and it shouldn't be too much work to add another one -- would you like to take a stab at it? here's where prepare-commit-msg was added for example: #1004

given the others are currently file-based there might need to be some design aspects to this particular hook since post-checkout doesn't really operate on files

[asottile]

oh right -- this got released as part of 2.2.0 -- thanks again for the issue!