chore: add a 'api contract' comment to MIS preamble (#850)

Author: palpatim

packages/appsync-modelgen-plugin/src/interfaces/introspection/model-schema.ts

@@ -1,3 +1,12 @@
+// This file defines the Model Introspection Schema contract between Amplify Data and its consumers, including:
+// - Gen1 CLI
+// - Gen1 Studio
+// - Gen2 CLI
+// - Gen2 Console
+// - Gen2 data-client
+//
+// Any change to this file represents a change in that API, and must be reviewed as such.
+
 /**
  * Root Schema Representation
  */
@@ -129,4 +138,4 @@ export type Argument = {
   isArray: boolean;
   isRequired: boolean;
   isArrayNullable?: boolean;
-}
+}