R1:b27fd05eef0a

Add a `bin/bulk export` CLI tool to make debugging and profiling large exports easier

Summary:
Ref T13049. When stuff executes asynchronously on the bulk workflow it can be hard to inspect directly, and/or a pain to test because you have to go through a bunch of steps to run it again.

Make future work here easier by making export triggerable from the CLI. This makes it easy to repeat, inspect with `--trace`, profile with `--xprofile`, etc.

Test Plan:
- Ran several invalid commands, got sensible error…