R1:30473549acfb

Add a basic pull event log for debugging repository cloning

Summary:
Ref T10228. This is currently quite limited:

- No UI.
- No SSH support.

My primary goal is to debug the issue in T10228. In the long run we can expand this to be a bit fancier.

Test Plan:
Made various valid and invalid clones, got sucess responses and not-so-successful responses, viewed the log table for general corresponding messages and broad sanity.

Ran GC via `bin/phd debug trigger`, no issues.

Reviewers: chad

Reviewed By…