Update .gitlab-ci.yml file

.gitlab-ci.yml

 stages:
+  - build_back
   - build_front
 
+
 build:
+  stage: build_back
+ 
+  script: echo "Building"
+  image:
+    name: gcr.io/kaniko-project/executor:debug
+    entrypoint: [""]
+  script:
+    - echo "{\"auths\":{\"$CI_REGISTRY\":{\"username\":\"$CI_REGISTRY_USER\",\"password\":\"$CI_REGISTRY_PASSWORD\"}}}" > /kaniko/.docker/config.json
+    - /kaniko/executor --context $CI_PROJECT_DIR/backend-express --dockerfile $CI_PROJECT_DIR/backend-express/Dockerfile --destination $CI_REGISTRY_IMAGE:backend
+#$CI_REGISTRY_IMAGE:$CI_COMMIT_TAG
+
   stage: build_front
  
   script: echo "Building"