Add dockerize stage and update GitLab CI pipeline

backend/.gitlab-ci.yml

@@ -1,15 +1,19 @@
 stages:
   - backend_build
+  - dockerize
 
 variables:
   REGISTRY: registry.gitlab.com/rheinsw/$CI_PROJECT_PATH
   TAG: $CI_COMMIT_REF_SLUG
 
+default:
+  before_script:
+    - cd backend
+
 backend_build_job:
   stage: backend_build
   image: maven:3.9.9-eclipse-temurin-21@sha256:2e3824afeb41f61761adee95318814e6669bd59aaf61255b2af47064b8755c02
   script:
-    - cd backend
     - mvn package
   artifacts:
     paths:
@@ -43,4 +47,4 @@ build_discovery_image:
     - docker push $REGISTRY/discovery-server:$TAG
   needs:
     - backend_build_job
-    - build_shared_base_image
+    - build_shared_base_image