feat(workers): worker operational state (#2427)

* feat(workers): worker operational state

internal/proto/controller/storage/servers/store/v1/worker.proto

@@ -58,6 +58,10 @@ message Worker {
   // The version of Boundary the worker binary is running
   // @inject_tag: `gorm:"default:null"`
   string release_version = 140;
+
+  // The state of the worker, to indicate if the worker is active or in shutdown.
+  // @inject_tag: `gorm:"not_null"`
+  string operational_state = 150;
 }
 
 // WorkerTag is a tag for a worker.  The primary key is comprised of the