SERVER-86295 adds the possibility to track and then move unsharded collections out of a shard. From a user's perspective, when removing a shard (or when transitioning to a dedicated config server) if the user wants to move the collections in an online fashion (as in, not with movePrimary) the user needs to know which collections must be moved.

The purpose of this ticket is to create a new command that given a shard the command will return the list of unsharded collections that needs to be moved to successfully remove the shard. As precondition, the shard must've been marked as drained, to prevent other migrations from moving collections to the shard.