refactor: simplify/improve status alert handling (#1519)

also adds new functionality to restore any pending down alerts
that were lost by hub restart before creation

internal/tests/hub.go

@@ -98,7 +98,7 @@ func ClearCollection(t testing.TB, app core.App, collectionName string) error {
 }
 
 func (h *TestHub) Cleanup() {
-	h.GetAlertManager().StopWorker()
+	h.GetAlertManager().Stop()
 	h.GetSystemManager().RemoveAllSystems()
 	h.TestApp.Cleanup()
 }