Add pre-commit support

[ilCatania]

Add support for running pytype as a pre-commit hook

[eggplants]

This feature has removed from repo in 41729ee. I don't know why.

@rchen152

[rchen152]

Apologies, that was a bad merge! I'll re-add .pre-commit-hooks.yaml and change our export rules so it doesn't get overwritten (i.e., deleted) again.