Add MyMDC check_connection action

See merge request detectors/pycalibration!520

webservice/webservice.py

@@ -752,10 +752,19 @@ class ActionsServer:
         'query-rid',
         'upload-yaml',
         'update_conf',
+        'check_connection',
     }
 
     # Handler methods for each available action ------------------------------
 
+    async def handle_check_connection(self, *args):
+        """Inform the caller that the service is up and running.
+
+        MyMDC will send the same information as provided to dark or correct
+        requests, but nothing is done with this information.
+        """
+        return b'success'
+
     async def handle_correct(
             self, rid, _sase, instrument, cycle, proposal, runnr, priority
     ):