R1:b4796d28374c

Add "Content type" and "Rule type" fields to Herald rules for Herald rules

Summary:
Depends on D19400. Ref T13130. Currently, when you write Herald rules about other Herald rules, you can't pick a rule type or content type, so there's no way to get notified about edits to just global rules (which is the primary driving use case).

Add a "Content type" field to let the rule match rules that affect revisions, tasks, commits, etc.

Add a "Rule type" field to let the rule match global, personal, or object…