Log Herald rules with invalid actions via phlog()

Summary:
When Herald rules fail unexpectedly due to relying on a (now) invalid action, 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 T15887

Test Plan: See steps in T15887; check error log.

Reviewers: O1 Blessed Committers, avivey

Reviewed By: O1 Blessed Committers, avivey

Subscribers: avivey, tobiaswiese, valerio.bozzolan, Matthew, Cigaryno

Maniphest Tasks: T15887

Differential Revision: https://we.phorge.it/D25737

src/applications/herald/engine/HeraldEngine.php

@@ -688,6 +688,14 @@ final class HeraldEngine extends Phobject {
         ->setTarget($action->getTarget())
         ->setRule($rule);
 
+      if ($object->getActionImplementation($action->getAction()) === null) {
+        phlog(pht('An exception occurred executing Herald rule %s: Unknown '.
+          'action: "%s". Review the Herald transcripts and correct or '.
+          'disable the problematic rule.',
+        $rule->getMonogram(),
+        $action->getAction()));
+      }
+
       $name = $rule->getName();
       $id = $rule->getID();
       $effect->setReason(