Expedited delete

See #9364, #9278, Expiring collections

Example use case: a user has stored a very large collection, then realized one or more of the following:
  • This data should not be stored here at all (uploaded the wrong files)
  • This data consumes too much space (disks are full)
  • This data costs too much to store (using too much cloud storage)

An admin should be able to delete the relevant blocks, bypassing the usual GC-race window, but (aside from that) in the safest possible way.