chore: stabilize appsync module

Change stability and maturity of `@aws-cdk/aws-appsync` constructs to
stable.

Fixes: #6836

packages/@aws-cdk/aws-appsync/README.md

@@ -9,13 +9,7 @@
 >
 > [CFN Resources]: https://docs.aws.amazon.com/cdk/latest/guide/constructs.html#constructs_lib
 
-![cdk-constructs: Experimental](https://img.shields.io/badge/cdk--constructs-experimental-important.svg?style=for-the-badge)
-
-> The APIs of higher level constructs in this module are experimental and under active development.
-> They are subject to non-backward compatible changes or removal in any future version. These are
-> not subject to the [Semantic Versioning](https://semver.org/) model and breaking changes will be
-> announced in the release notes. This means that while you may use them, you may need to update
-> your source code when upgrading to a newer version of this package.
+![cdk-constructs: Stable](https://img.shields.io/badge/cdk--constructs-stable-success.svg?style=for-the-badge)
 
 ---
 

packages/@aws-cdk/aws-appsync/package.json

@@ -136,8 +136,8 @@
       "props-physical-name:@aws-cdk/aws-appsync.AppsyncFunctionProps"
     ]
   },
-  "stability": "experimental",
-  "maturity": "experimental",
+  "stability": "stable",
+  "maturity": "stable",
   "awscdkio": {
     "announce": false
   },