Command clean up goroutines stay around until context cancellation even if the command is finished

The clean up goroutines launched on command invocations do not finish when the command is finished and stay around until the context is canceled. This can lead to piling up a lot of these goroutines during RPC calls which invoke a lot of commands. One such example if UpdateRemoteMirror which launches potentially a lot of commands to check commit ancestorship. While we should fix such RPCs to reuse the process for multiple checks if possible, we also shouldn't leave these goroutines running longer than necessary.

Problem with UpdateRemoteMirror #4180 (comment 924370321)