Add Java 21 to universal container (#865)

* Add Java 21 to universal container

* The universal image only supports the two latest LTS versions

Co-authored-by: Samruddhi Khandale <samruddhikhandale@github.com>

---------

Co-authored-by: Samruddhi Khandale <samruddhikhandale@github.com>

Author: timward60

src/universal/.devcontainer/devcontainer.json

@@ -43,8 +43,8 @@
             "additionalVersions": "3.1"
         },
         "ghcr.io/devcontainers/features/java:1": {
-            "version": "17",
-            "additionalVersions": "11",
+            "version": "21",
+            "additionalVersions": "17",
             "installGradle": "true",
             "installMaven": "true"
         },