fix: missing 404 response in rule engine api schema

apps/emqx_rule_engine/src/emqx_rule_engine_api.erl

@@ -253,6 +253,7 @@ schema("/rules/:id") ->
             summary => <<"Delete rule">>,
             parameters => param_path_id(),
             responses => #{
+                404 => error_schema('NOT_FOUND', "Rule not found"),
                 204 => <<"Delete rule successfully">>
             }
         }