ci: add image building

.gitlab-ci.yml

@@ -0,0 +1,22 @@
+image: docker:stable
+
+stages:
+  - image
+
+docker image:
+  stage: image
+  only:
+    variables:
+      - $BUILD_IMAGE == "true"
+  variables:
+    DOCKER_DRIVER: overlay2
+  services:
+    - docker:dind
+  script:
+    - docker login -u gitlab-ci-token -p $CI_JOB_TOKEN registry.gitlab.com
+    - docker build -t registry.gitlab.com/openstapps/app-release-template .
+    - docker push registry.gitlab.com/openstapps/app-release-template
+  only:
+    - main
+  tags:
+    - docker