query<T>  abstract method 
Implementation
Future<GraphQLResponse<T>> query<T>(
  String query, {
  String? url,
  Map<String, dynamic>? variables,
  Map<String, String>? headers,
});Future<GraphQLResponse<T>> query<T>(
  String query, {
  String? url,
  Map<String, dynamic>? variables,
  Map<String, String>? headers,
});