0.2.20230124-124516-h352feeef

mirror: Log less and make concurrency customisable

Summary:
Slices were very noisy, so I made them log less.

Plus now you can specify the concurrency of the command via CLI args. I tweaked it and saw no improvements though :(

Reviewed By: markbt

Differential Revision: D42683915

fbshipit-source-id: 5930a44c6a24fd48560512dd83a630c283c9a351