Enhance PlugNMeet client error logging to include status code and body details

apps/course/services/plugnmeet.py

@@ -102,8 +102,9 @@ class PlugNMeetClient:
 
         if response.status_code >= 400:
             response_data = self._safe_json(response)
+            error_msg = f"PlugNMeet server returned status {response.status_code}: {response.text}"
             raise PlugNMeetError(
-                "PlugNMeet server returned an error.",
+                error_msg,
                 status_code=response.status_code,
                 response_data=response_data,
             )