chore(redshift): update package stability to experimental (aws#10983)

L2 constructs were created in May for this module, but the package stability was
never updated.

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

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

@@ -1,11 +1,16 @@
 ## Amazon Redshift Construct Library
+
 <!--BEGIN STABILITY BANNER-->
 ---
 
 ![cfn-resources: Stable](https://img.shields.io/badge/cfn--resources-stable-success.svg?style=for-the-badge)
 
 > All classes with the `Cfn` prefix in this module ([CFN Resources](https://docs.aws.amazon.com/cdk/latest/guide/constructs.html#constructs_lib)) are always stable and safe to use.
 
+![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 This means that while you may use them, you may need to update your source code when upgrading to a newer version of this package.
+
 ---
 <!--END STABILITY BANNER-->
 
@@ -24,6 +29,7 @@ const cluster = new redshift.Cluster(this, 'Redshift', {
     vpc
   });
 ```
+
 By default, the master password will be generated and stored in AWS Secrets Manager.
 
 A default database named `default_db` will be created in the cluster. To change the name of this database set the `defaultDatabaseName` attribute in the constructor properties.
@@ -46,11 +52,13 @@ cluster.clusterEndpoint.socketAddress;   // "HOSTNAME:PORT"
 ### Rotating credentials
 
 When the master password is generated and stored in AWS Secrets Manager, it can be rotated automatically:
+
 ```ts
 cluster.addRotationSingleUser(); // Will rotate automatically after 30 days
 ```
 
 The multi user rotation scheme is also available:
+
 ```ts
 cluster.addRotationMultiUser('MyUser', {
   secret: myImportedSecret

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

@@ -111,7 +111,7 @@
     ]
   },
   "stability": "experimental",
-  "maturity": "cfn-only",
+  "maturity": "experimental",
   "awscdkio": {
     "announce": false
   }