Move grpc server watcher to workspace rather than repo location
Summary: This allows the repo locations to recover when they transition from working => error => working again
Test Plan: BK, run a grpc server against dagit, bring it down, update dagit, bring it back up, update dagit
Reviewers: sashank, alangenfeld
Reviewed By: sashank
Differential Revision: https://dagster.phacility.com/D7705