Add docker build to CI

.gitlab-ci.yml

 stages:
-  - update
-  - build
+  - ⏫ Update
+  - 🏗️ Build
 
 variables:
   DOCKER_IMAGE: cverstege/alma9-base
-  DOCKER_TAG: latest
 
 before_script:
   - apt-get update && apt-get install -y curl git
 
-update_dockerfile:
-  stage: update
+Update Upstream 🛠️:
+  stage: ⏫ Update
   script:
     - ./alma9-base/update.sh
     - git config user.name "CI Pipeline"
     - git config user.email "cedric.verstege@kit.edu"
     - git add alma9-base/Dockerfile
-    - git commit -m "Update upstream to version $(grep -oP "FROM cern/alma9-base:\K[\w.-]+" "alma9-base/Dockerfile")"
+    - git commit -m "⏫ Update upstream to version $(grep -oP "FROM cern/alma9-base:\K[\w.-]+" "alma9-base/Dockerfile")"
     - git remote set-url --push origin "https://$CI_COMMITTER_USER_AND_TOKEN@gitlab.etp.kit.edu/cverstege/docker-images.git"
     - git push origin HEAD:$CI_COMMIT_REF_NAME
   rules:
@@ -25,3 +24,12 @@ update_dockerfile:
       allow_failure: false
     - when: manual
       allow_failure: true
+
+Build Docker Image:
+  stage: 🏗️ Build
+  image:
+    name: docker:dind
+  script:
+    - docker build -t $DOCKER_IMAGE:$(grep -oP "FROM cern/alma9-base:\K[\w.-]+" "alma9-base/Dockerfile") $DOCKER_IMAGE:latest alma9-base
+    - docker login -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD
+    - docker push cverstege/alma9-base --all-tags