Update gitpod Dockerfile to 21.0.2-tem (#2555)

Author: sfeilmeier

.gitpod.Dockerfile

@@ -1,7 +1,7 @@
 FROM gitpod/workspace-postgres
 
 RUN bash -c ". /home/gitpod/.sdkman/bin/sdkman-init.sh \
-             && sdk install java 17.0.6-tem"
+             && sdk install java 21.0.2-tem"
 
 # disable angular analytics
 ENV NG_CLI_ANALYTICS=false