Add sign in with apple to Flutter reference docs

spec/common-client-libs-sections.json

@@ -425,6 +425,13 @@
         "product": "auth",
         "type": "function"
       },
+      {
+        "id": "sign-in-with-apple",
+        "title": "Sign in with Apple",
+        "slug": "sign-in-with-apple",
+        "product": "auth",
+        "type": "function"
+      },
       {
         "id": "sign-in-with-oauth",
         "title": "Sign in a user through OAuth",

spec/supabase_dart_v1.yml

@@ -165,6 +165,22 @@ functions:
             phone: '+13334445555',
           );
           ```
+  - id: sign-in-with-apple
+    title: 'signInWithApple()'
+    description: |
+      Signs in a user using native Apple login.
+    notes: |
+      - You need to [register your bundle ID](https://developer.apple.com/help/account/manage-identifiers/register-an-app-id/) and add it to Supabase dashboard.
+      - This method is only available in iOS and MacOS
+      - For other platforms, [signInWithOAuth()](https://supabase.com/docs/reference/dart/auth-signinwithoauth) should be used.
+    examples:
+      - id: sign-in-with-apple
+        name: Sign in with Apple
+        isSpotlight: true
+        code: |
+          ```dart
+          final AuthResponse = await supabase.auth.signInWithApple();
+          ```
   - id: sign-in-with-oauth
     title: 'signInWithOAuth()'
     description: |