Add 'session_id' to server lost during query error msg

If multiple backend connections are lost at the same time, the same
message will appear multiple times, one per backend connection that was
lost during a query, this info wasn't reflected in the msg before.

lib/MySQL_Session.cpp

@@ -4370,11 +4370,11 @@ int MySQL_Session::handler_ProcessingQueryError_CheckBackendConnectionStatus(MyS
 		bool retry_conn=false;
 		if (myconn->server_status==MYSQL_SERVER_STATUS_SHUNNED_REPLICATION_LAG) {
 			thread->status_variables.stvar[st_var_backend_lagging_during_query]++;
-			proxy_error("Detected a lagging server during query: %s, %d\n", myconn->parent->address, myconn->parent->port);
+			proxy_error("Detected a lagging server during query: %s, %d, session_id:%u\n", myconn->parent->address, myconn->parent->port, this->thread_session_id);
 			MyHGM->p_update_mysql_error_counter(p_mysql_error_type::proxysql, myconn->parent->myhgc->hid, myconn->parent->address, myconn->parent->port, ER_PROXYSQL_LAGGING_SRV);
 		} else {
 			thread->status_variables.stvar[st_var_backend_offline_during_query]++;
-			proxy_error("Detected an offline server during query: %s, %d\n", myconn->parent->address, myconn->parent->port);
+			proxy_error("Detected an offline server during query: %s, %d, session_id:%u\n", myconn->parent->address, myconn->parent->port, this->thread_session_id);
 			MyHGM->p_update_mysql_error_counter(p_mysql_error_type::proxysql, myconn->parent->myhgc->hid, myconn->parent->address, myconn->parent->port, ER_PROXYSQL_OFFLINE_SRV);
 		}
 		if (myds->query_retries_on_failure > 0) {