Allow users to override federated timeline removal

I aggressively prune things from the federated timeline (big generalist instances, places that aren’t really objectionable but don’t CW stuff our users are used to seeing CW’d etc.) and many of my users seem to like it (they’ve commented on liking that the federated timeline is actually useful.)

However, as an admin, I would really like it if users had some means to un-remove things from the federated timeline if they liked.

this is likely not going to happen - it adds yet another layer of complexity to the already complex timeline query, and admin actions should always override user actions