Use Docker caching like recommended by the docs

See: https://docs.gitlab.com/ee/ci/docker/docker_layer_caching.html

Author: MrEbbinghaus

.gitlab-ci.yml

@@ -60,7 +60,10 @@ build_latest_images:
   before_script:
     - docker login -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD $CI_REGISTRY
   script:
-    - docker build -t $CI_REGISTRY_IMAGE:staging .
+    - docker pull $CI_REGISTRY_IMAGE:latest || true
+    - docker build --cache-from $CI_REGISTRY_IMAGE:latest --tag $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA --tag $CI_REGISTRY_IMAGE:latest --tag $CI_REGISTRY_IMAGE:staging .
+    - docker push $CI_REGISTRY_IMAGE:latest
+    - docker push $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA
     - docker push $CI_REGISTRY_IMAGE:staging
   rules:
     - if: $CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH