Whatsnew fix (#8509)

* Fixed whatsnew to include Cloud Docker 1.2.1 release

* Simplied github entry

* Update src/_data/whats-new.yml

Co-authored-by: Shrie Spangler <spangler@adobe.com>

* Fixed github entry and changed link per review

Co-authored-by: Shrie Spangler <spangler@adobe.com>

Author: bdenham

src/_data/whats-new.yml

@@ -14,6 +14,13 @@ entries:
   link: https://github.com/magento/devdocs/pull/8488
   contributor: jeff-matthews
   profile: https://github.com/jeff-matthews
+- description: Published release notes for [Cloud Docker 1.2.1](https://devdocs.magento.com/cloud/release-notes/mcd-release-notes.html#v121).
+  versions: 2.4.x
+  type: Major Update
+  date: December 22, 2020
+  link: https://github.com/magento/devdocs/pull/8429
+  contributor: bdenham
+  profile: https://github.com/bdenham
 - description: Added a new topic with instructions for [reverting from a split database
     to a single database](https://devdocs.magento.com/guides/v2.4/config-guide/revert-split-database.html)
     implementation.