Adds the commit sha to the pushed assets

* This will upload the sha of the docker image containing assets to
  assist with building specific sha builds in the future.
* Addresses: https://gitlab.com/gitlab-org/release/framework/issues/51

scripts/build_assets_image

@@ -22,6 +22,8 @@ mkdir -p assets_container.build/public
 cp -r public/assets assets_container.build/public/
 cp Dockerfile.assets assets_container.build/
 docker build -t ${ASSETS_IMAGE_PATH}:${CI_COMMIT_REF_SLUG} -f assets_container.build/Dockerfile.assets assets_container.build/
+docker tag ${ASSETS_IMAGE_PATH}:${CI_COMMIT_REF_SLUG} ${ASSETS_IMAGE_PATH}:${CI_COMMIT_SHA}
 docker login -u gitlab-ci-token -p ${CI_JOB_TOKEN} ${CI_REGISTRY}
-docker push ${ASSETS_IMAGE_PATH}
+docker push ${ASSETS_IMAGE_PATH}:${CI_COMMIT_REF_SLUG}
+docker push ${ASSETS_IMAGE_PATH}:${CI_COMMIT_SHA}