R1:bacf1f44e00f

Modularize HeraldRule transactions

Summary:
Ref T13249. See PHI1115. I initially wanted to make `bin/policy unlock --owner <user> H123` work to transfer ownership of a Herald rule, although I'm no longer really sure this makes much sense.

In any case, this makes things a little better and more modern.

I removed the storage table for rule comments. Adding comments to Herald rules doesn't work and probably doesn't make much sense.

Test Plan: Created and edited Herald rules, grepped for all the…