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/macos/Runner/GoogleService-Info.plist

@@ -0,0 +1,30 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+	<key>API_KEY</key>
+	<string>AIzaSyBNEtAHdjm3oFV6JZ6nbx5t6Pfyj4w4hbo</string>
+	<key>GCM_SENDER_ID</key>
+	<string>44885228795</string>
+	<key>PLIST_VERSION</key>
+	<string>1</string>
+	<key>BUNDLE_ID</key>
+	<string>com.example.geminiIoTalk.RunnerTests</string>
+	<key>PROJECT_ID</key>
+	<string>gemini-cat-chef</string>
+	<key>STORAGE_BUCKET</key>
+	<string>gemini-cat-chef.appspot.com</string>
+	<key>IS_ADS_ENABLED</key>
+	<false></false>
+	<key>IS_ANALYTICS_ENABLED</key>
+	<false></false>
+	<key>IS_APPINVITE_ENABLED</key>
+	<true></true>
+	<key>IS_GCM_ENABLED</key>
+	<true></true>
+	<key>IS_SIGNIN_ENABLED</key>
+	<true></true>
+	<key>GOOGLE_APP_ID</key>
+	<string>1:44885228795:ios:9585fdfdf50acdd18f845e</string>
+</dict>
+</plist>