Add Auto Archive Duration Option for Only after Event Ends

Right now there's only a 24 hr, 3 day, and 1 week option for auto archive of any thread. This doesn't make any sense for events that users want to plan in advance. My friends easily will plan events most of our in-person events 1-2 months in advance so we don't want these threads to auto hide or people will forget they joined the event. These should only hide after the event is scheduled to end.