tag a docker image by date

.gitlab-ci.yml

 variables:
-  IMAGE: rwthos/hermitcore-rs
+  IMAGE: rwthos/hermit-cargo
   GIT_SUBMODULE_STRATEGY: normal
+  VERSION=$(date %Y%m%d%H%M%S)
 
 stages:
   - prepare
@@ -13,7 +14,9 @@ docker:
   script:
     - docker build -t ${IMAGE} .
     - docker tag ${IMAGE} ${IMAGE}:latest
+    - docker tag ${IMAGE} ${IMAGE}:${VERSION}
     - docker push ${IMAGE}:latest
+    - docker push ${IMAGE}:${VERSION}
   tags:
     - shell
     - linux