Log Herald rules with invalid keys via phlog()
Summary:
When Herald rules fail unexpectedly due to relying on a (now) invalid key, allow Phorge administrators to get aware by creating an entry in the error log via `phlog()` instead of crossing fingers that someone may from time to time get the idea to open and read Herald transcripts.
Refs T15885
Test Plan: See steps in T15885; check error log.
Reviewers: O1 Blessed Committers, valerio.bozzolan
Reviewed By: O1 Blessed Committers, valerio.bozzolan
Subscribers: tobiaswiese, valerio.bozzolan, Matthew, Cigaryno
Maniphest Tasks: T15885
Differential Revision: https://we.phorge.it/D25735