DOCSP-30261: fix link to Atlas Serverless product (#408)

(cherry picked from commit 1099c2b)

Author: Chris Cho

source/whats-new.txt

@@ -60,7 +60,7 @@ New features of the 4.3 Java driver release include:
      naming change.
 
 - Added support for connection to
-  `MongoDB Atlas Serverless Instances <https://www.mongodb.com/cloud/atlas/serverless>`__.
+  `MongoDB Atlas Serverless Instances <https://www.mongodb.com/use-cases/serverless>`__.
   For more information on setup, see our documentation on how to
   :atlas:`Create a New Serverless Instance </tutorial/create-new-serverless-instance/?jmp=docs_driver_java>`
 - Added a builder API for the ``setWindowFields`` pipeline stage to allow the use of window operators