SERVER-133518 implemented a workaround to make sharding coordinators release locks during stepdown.

Ideally, cleanup work should not be inline in the stepdown path, and should instead be executed asynchronously, or during a potential next stepup.

This ticket tracks the work to improve the cleanup of sharding coordinators, making stepdown start an asynchronous job that will interrupt and join leftovers (including releasing the locks) initiated via stepdown. That way, the SERVER-133518 workaround can go away.

Stepup will just need to wait for that future to finish, instead of doing exactly that work.