Inserted RefreshStream legacy example in its stand alone folder

legacy/refresh_stream/lib/auth.dart

@@ -0,0 +1,22 @@
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+
+class AuthNotifier extends StateNotifier<bool> {
+  AuthNotifier() : super(false);
+
+  /// This mocks a login attempt with email and password
+  Future<void> login(String email, String password) async {
+    state = await Future.delayed(
+      const Duration(milliseconds: 750),
+      () => true,
+    );
+  }
+
+  /// This mocks a logout action
+  Future<void> logout() async {
+    state = false; // No request is mocked here but I guess we could
+  }
+}
+
+final authProvider = StateNotifierProvider<AuthNotifier, bool>((ref) {
+  return AuthNotifier();
+});