Draft: implement object_reference operations in all backends

This implements !1042 (merged) for all the storage backends. Only the last few commits are really in this MR.

Ref. #4680 (closed) Ref. #4681 (closed) Ref. #4682 Ref. #4683 (closed)

The amount of data returned should be fairly small, so pagination was not implemented, only limiting.

Cc. @vlorentz