When archiving a project tag, active Herald rules using that very project in its conditions may remain active. Thus add an informational message about the specific affected Herald rules to the "Archive this project?" dialog which allows folks to realize that further actions may be welcome.

Closes T15996

1. Set up a project tag.
2. Set up two Herald rules which use that project tag in their conditions.
3. As a member of the "Can Use Application" group defined on http://phorge.localhost/applications/view/PhabricatorHeraldApplication/ and as a member of the "Can Create Projects" group defined on http://phorge.localhost/applications/view/PhabricatorProjectApplication/, go to http://phorge.localhost/project/manage/1/ and click Archive project. Check the dialog text and see the link to the affected Herald rules, for convenience.
4. As a non-member of the "Can Use Application" group defined on http://phorge.localhost/applications/view/PhabricatorHeraldApplication/ and as a member of the "Can Create Projects" group defined on http://phorge.localhost/applications/view/PhabricatorProjectApplication/, go to http://phorge.localhost/project/manage/1/ and click Archive project. Check the dialog text and see no link to the affected Herald rules and a message to contact your Herald magician. (Note that we expose IDs of Herald rules here to the public - I assume that is okay.)
5. Archive one of the two Herald rules, perform previous steps to check that the dialog now mentions one instead of two rules.
6. Archive both Herald rules, perform previous steps to check that the dialog now falls back to the previous default, not mentioning Herald rules at all.
7. After archiving a project, see that the Activate Project dialog on the project page is not affected.

Before you ask: No this cannot easily be applied also to Herald actions (instead of conditions) as there's no code similar to HeraldRuleQuery->withAffectedObjectPHIDs() for that.