Log commands that the interchange does not recognise, as an error (#3434

)

The interchange command protocol is tied to the submit side closely, and
it is generally a programmer or deployment error rather than intentional
cross-version compatibility that would result in this unknown command code
path firing.

parsl/executors/high_throughput/interchange.py

@@ -329,6 +329,7 @@ def _command_server(self) -> NoReturn:
                     reply = None
 
                 else:
+                    logger.error(f"Received unknown command: {command_req}")
                     reply = None
 
                 logger.debug("Reply: {}".format(reply))