document how to map appsync scalars to kotlin types

Author: tjroach

src/pages/[platform]/build-a-backend/data/aws-appsync-apollo-extensions/index.mdx

@@ -322,6 +322,23 @@ You can alternatively download the introspection schema using the [`fetch-schema
 4. Add this file to your project as directed by [Apollo documentation](https://www.apollographql.com/docs/kotlin/advanced/plugin-recipes#specifying-the-schema-location) 
 </InlineFilter>
 
+## Type Mapping AppSync Scalars
+By default, [AppSync Scalars](https://docs.aws.amazon.com/appsync/latest/devguide/scalars.html#graph-ql-aws-appsync-scalars) will default to the `Any` type.
+You can map these scalars to more explicit types by editing the `apollo` block in your `app/build.gradle[.kts]` file. In the example below, we 
+are now mapping a few of our AppSync scalar types to `String` instead of `Any`. Additional improvements could 
+made writing [custom class adapters](https://www.apollographql.com/docs/kotlin/essentials/custom-scalars#define-class-mapping) to convert date/time scalars 
+into Kotlin date/time class types.
+
+```kotlin
+apollo {
+    service("{serviceName}") {
+        packageName.set("{packageName}")
+        mapScalarToKotlinString("AWSDateTime")
+        mapScalarToKotlinString("AWSEmail")
+    }
+}
+```
+
 ### Performing Queries, Mutations, and Subscriptions with Apollo client
 
 1. Navigate to the **Queries** tab in your API on the [AWS AppSync console](https://console.aws.amazon.com/appsync/home). Here, you can test queries, mutations, and subscriptions in the GraphQL playground.