Introduce a new interface for storage with an id shared with multiple storages #30630
Description
Downside is that we introduce groupfolder specific implementation inside the server repo.
That was the case before already, now it is just differently implemented. Nevertheless, perhaps as a follow up to server 24 only? it would be good to have a storage agnostic solution to do the right thing. It could also be an additional interface that can be tested against.
Originally posted by @blizzz in #30531 (comment)