groupAsync method
Asynchronous equivalent of group.
Implementation
Future<SymlinkRoute<T>> groupAsync(
String path, FutureOr<void> Function(Router<T> router) callback,
{Iterable<T> middleware = const [], String name = ''}) async {
final router = Router<T>().._middleware.addAll(middleware);
await callback(router);
return mount(path, router)..name = name;
}