Log exception for webhook worker

.warning sometimes shows empty message rather than actual error

mapadroid/webhook/webhookworker.py

@@ -120,6 +120,7 @@ async def __send_webhook(self, payloads):
                                        whcount_text, await mad_json_dumps(self.__payload_type_count(payload_chunk)))
                 except Exception as e:
                     logger.warning("Exception occured while sending webhook: {}", e)
+                    logger.exception(e)
 
                 current_pl_num += 1
             current_wh_num += 1