OZG-7491 pipeline: Enable gitlab image push

.gitlab-ci.yml

@@ -70,7 +70,7 @@ push-merge-request-image-gitlab:
     - mvn deploy -Pgitlab-deploy $MAVEN_DEPLOY_CLI_OPTS $MAVEN_CLI_OPTS
   rules:
     - if: $CI_PIPELINE_SOURCE == 'merge_request_event'
-      when: never  # Step disabled until gitlab container registry works
+      when: manual
 
 push-merge-request-image-nexus:
   stage: publish