Adds ai_recipe_generation sample (#2242)

Adding the demo app from my I/O talk. Because AI.

## Pre-launch Checklist

- [x] I read the [Flutter Style Guide] _recently_, and have followed its
advice.
- [x] I signed the [CLA].
- [x] I read the [Contributors Guide].
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] All existing and new tests are passing.

---------

Co-authored-by: Brett Morgan <brett.morgan@gmail.com>

ai_recipe_generation/lib/firebase_options.dart

@@ -0,0 +1,81 @@
+// File generated by FlutterFire CLI.
+// ignore_for_file: lines_longer_than_80_chars, avoid_classes_with_only_static_members
+import 'package:firebase_core/firebase_core.dart' show FirebaseOptions;
+import 'package:flutter/foundation.dart'
+    show defaultTargetPlatform, kIsWeb, TargetPlatform;
+
+/// Default [FirebaseOptions] for use with your Firebase apps.
+///
+/// Example:
+/// ```dart
+/// import 'firebase_options.dart';
+/// // ...
+/// await Firebase.initializeApp(
+///   options: DefaultFirebaseOptions.currentPlatform,
+/// );
+/// ```
+class DefaultFirebaseOptions {
+  static FirebaseOptions get currentPlatform {
+    if (kIsWeb) {
+      return web;
+    }
+    switch (defaultTargetPlatform) {
+      case TargetPlatform.android:
+        return android;
+      case TargetPlatform.iOS:
+        return ios;
+      case TargetPlatform.macOS:
+        return macos;
+      case TargetPlatform.windows:
+        throw UnsupportedError(
+          'DefaultFirebaseOptions have not been configured for windows - '
+          'you can reconfigure this by running the FlutterFire CLI again.',
+        );
+      case TargetPlatform.linux:
+        throw UnsupportedError(
+          'DefaultFirebaseOptions have not been configured for linux - '
+          'you can reconfigure this by running the FlutterFire CLI again.',
+        );
+      default:
+        throw UnsupportedError(
+          'DefaultFirebaseOptions are not supported for this platform.',
+        );
+    }
+  }
+
+  static const FirebaseOptions web = FirebaseOptions(
+    apiKey: 'FIREBASE API KEY',
+    appId: 'FIREBASE APP ID',
+    messagingSenderId: 'FIREBASE MESSAGING ID',
+    projectId: 'PROJECT ID',
+    authDomain: 'AUTH DOMAIN',
+    storageBucket: 'STORAGE BUCKET ID',
+  );
+
+  static const FirebaseOptions android = FirebaseOptions(
+    apiKey: 'FIREBASE API KEY',
+    appId: 'FIREBASE APP ID',
+    messagingSenderId: 'FIREBASE MESSAGING ID',
+    projectId: 'PROJECT ID',
+    authDomain: 'AUTH DOMAIN',
+    storageBucket: 'STORAGE BUCKET ID',
+  );
+
+  static const FirebaseOptions ios = FirebaseOptions(
+    apiKey: 'FIREBASE API KEY',
+    appId: 'FIREBASE APP ID',
+    messagingSenderId: 'FIREBASE MESSAGING ID',
+    projectId: 'PROJECT ID',
+    authDomain: 'AUTH DOMAIN',
+    storageBucket: 'STORAGE BUCKET ID',
+  );
+
+  static const FirebaseOptions macos = FirebaseOptions(
+    apiKey: 'FIREBASE API KEY',
+    appId: 'FIREBASE APP ID',
+    messagingSenderId: 'FIREBASE MESSAGING ID',
+    projectId: 'PROJECT ID',
+    authDomain: 'AUTH DOMAIN',
+    storageBucket: 'STORAGE BUCKET ID',
+  );
+}