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/pubspec.yaml

@@ -0,0 +1,40 @@
+name: ai_recipe_generation
+description: "A new Flutter project."
+publish_to: 'none'
+version: 0.1.0
+
+environment:
+  sdk: '>=3.2.3 <4.0.0'
+
+dependencies:
+  async: ^2.11.0
+  camera: ^0.10.5+9
+  cloud_firestore: ^4.15.7
+  device_info_plus: ^9.1.2
+  firebase_core: ^2.26.0
+  flutter:
+    sdk: flutter
+  flutter_floating_bottom_bar: ^1.2.0
+  flutter_markdown: ^0.6.20
+  flutter_svg: ^2.0.9
+  google_fonts: 6.1.0
+  google_generative_ai: ^0.2.0
+  image_picker: ^1.0.7
+  material_symbols_icons: ^4.2719.1
+  path: ^1.9.0
+  path_provider: ^2.1.2
+  provider: ^6.1.1
+  shared_preferences: ^2.2.2
+  sticky_headers: ^0.3.0+2
+
+dev_dependencies:
+  flutter_test:
+    sdk: flutter
+  analysis_defaults:
+    path: ../analysis_defaults
+
+flutter:
+  uses-material-design: true
+
+  assets:
+    - assets/