[feature] Automatically reject pending follow requests after x amount of time (ie., reject "stale" follow requests)

[tsmethurst]

Relates to #2677.

Really large follow request queues can be intimidating. One way to handle this would be to automatically reject follow requests if they've been sitting around for longer than maybe a week, or some other user-customizable "freshness/staleness" amount. We could also make this conditional: only reject "stale" follow requests if they're from someone the user doesn't follow, that is, inbound follow requests from someone the user themself follows should not become "stale" because they're more interesting potential relationships.