Migrate to jdk 21 (#2295)

* docker containers using images with jre 21
* project is still building with target java 17 - so jar artifacts are java 17 compatible
* provided option to have different version for client libraries (e.g. ddi and management REST api)

Signed-off-by: Avgustin Marinov <Avgustin.Marinov@bosch.com>

.github/workflows/trivy-scan.yml

@@ -29,7 +29,7 @@ jobs:
         uses: actions/setup-java@v4
         with:
           distribution: "temurin"
-          java-version: "17"
+          java-version: 21
           cache: "maven"
 
       - name: Create hawkBit container images