chore(chatbot): update module stability to experimental instead of cf…

…n-only (#10880)

L2 constructs were introduced last month in #9702 for slack channel
configuration. marking the module as experimental to reflect that
the module is no longer cfn-only.

----

*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-chatbot/README.md

@@ -6,6 +6,10 @@
 
 > 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 This means that while you may use them, you may need to update your source code when upgrading to a newer version of this package.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-->
 

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

@@ -99,7 +99,7 @@
     "node": ">= 10.13.0 <13 || >=13.7.0"
   },
   "stability": "experimental",
-  "maturity": "cfn-only",
+  "maturity": "experimental",
   "awscdkio": {
     "announce": false
   }