R1:bd29784a32cf

Add an administrative `bin/repository importing` command to list importing commits

Summary: Ref T4068. Adds a command to list all commits in an "importing" status. This will allow users to use `reparse.php` to diagnose and repair issues.

Test Plan:
- Ran `bin/repository importing P`, etc.
- Used `reparse.php` to reparse some commit stages and saw status update correctly.
- Ran on a repo with no importing commits.
- Ran with `... --simple | xargs`, which saves us having to put an `awk` or…