chore(synthetics): deprecate aws-synthetics-alpha (#27471)

Depends on #27470.

Deprecates the alpha module for aws-synthetics-alpha so that the last version of aws-synthetics-alpha points to the stable aws-cdk-lib/aws-synthetics.

----

*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-synthetics-alpha/README.md

@@ -3,18 +3,16 @@
 
 ---
 
-![cdk-constructs: Developer Preview](https://img.shields.io/badge/cdk--constructs-developer--preview-informational.svg?style=for-the-badge)
+![Deprecated](https://img.shields.io/badge/deprecated-critical.svg?style=for-the-badge)
 
-> The APIs of higher level constructs in this module are in **developer preview** before they
-> become stable. We will only make breaking changes to address unforeseen API issues. Therefore,
-> these APIs are not subject to [Semantic Versioning](https://semver.org/), and breaking changes
-> will be announced in 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 update your source code when upgrading to a newer version of this package.
+> This API may emit warnings. Backward compatibility is not guaranteed.
 
 ---
 
 <!--END STABILITY BANNER-->
 
+All constructs moved to aws-cdk-lib/aws-synthetics.
+
 Amazon CloudWatch Synthetics allow you to monitor your application by generating **synthetic** traffic. The traffic is produced by a **canary**: a configurable script that runs on a schedule. You configure the canary script to follow the same routes and perform the same actions as a user, which allows you to continually verify your user experience even when you don't have any traffic on your applications.
 
 ## Canary

packages/@aws-cdk/aws-synthetics-alpha/package.json

@@ -2,7 +2,7 @@
   "name": "@aws-cdk/aws-synthetics-alpha",
   "version": "0.0.0",
   "private": false,
-  "description": "The CDK Construct Library for AWS::Synthetics",
+  "description": "This module is deprecated. All constructs are now available under aws-cdk-lib/aws-synthetics",
   "main": "lib/index.js",
   "types": "lib/index.d.ts",
   "jsii": {
@@ -104,8 +104,8 @@
   "engines": {
     "node": ">= 14.15.0"
   },
-  "stability": "experimental",
-  "maturity": "developer-preview",
+  "stability": "deprecated",
+  "maturity": "deprecated",
   "awscdkio": {
     "announce": false
   },
@@ -117,5 +117,6 @@
       "naming/package-matches-directory",
       "assert/assert-dependency"
     ]
-  }
+  },
+  "deprecated": "This package has been stabilized in aws-cdk-lib is no longer being updated under the -alpha name. Users should migrate to aws-<module> in aws-cdk-lib."
 }