listen for shutdown signals during nym-node startup (#5879)

this is to avoid situation where the process can't be killed without 'kill -9' because the logic to listen to shutdown signals hasn't been hit yet

gateway/src/node/internal_service_providers.rs

@@ -128,6 +128,8 @@ where
             }
         });
 
+        // TODO: if something is blocking during SP startup, the below will wait forever
+        // we need to introduce additional timeouts here.
         let on_start_data = self
             .on_start_rx
             .await