Check repo size and enforce a limit before cloning

some small minority of git repos are enormous

We could have a setting that institutes a maximum per repo clone size to help avoid disk space inflating too fast.

github offers a `size` parameter (in Kb) in its API. This, in practice can be either very close to, or very far from the actual clone size as github is measuring from a bare repo.

I would either add between a 50-100% safety margin or just have the filtering be based on the reported size.

Users may prefer the first one since their specified value will be closer to an actual real limit thats comparable to their "available disk space" stats