Add docker login step

.gitlab-ci.yml

@@ -3,6 +3,9 @@
 build-esa:
   stage: build
 
+  before_script:
+    - docker login -u "$CI_REGISTRY_USER" -p "$CI_REGISTRY_PASSWORD" $CI_REGISTRY
+
   script:
     - docker build --pull -t "$CI_REGISTRY/$CI_PROJECT_PATH:latest" .
     - docker push "$CI_REGISTRY/$CI_PROJECT_PATH:latest"