[hma] "Negative" Hash banks - Banks that allow ignoring or preventing match events

[Dcallies]

This is a feature that has been mentioned a few times, and can help deal with benign content.

The idea is a type of bank where the presence of content in the bank subtracts the match events from other banks. This allows allowlisting benign content or other collision prone hashes.

Open Questions

• Should this be a global ignore, or should we require that you specify the banks that you are suppressing