add dockerized build in CI pipeline

.gitlab-ci.yml

+---
+
+build::image:
+  image: docker:19.03.12
+  stage: build
+  tags:
+    - dind
+  before_script:
+    - echo ${CI_REGISTRY}
+    - docker login -u ${CI_REGISTRY_USER} -p ${CI_REGISTRY_PASSWORD} ${CI_REGISTRY}
+  script:
+    - docker build --pull -t ${CI_REGISTRY_IMAGE}:${CI_COMMIT_REF_SLUG} .
+    - docker push ${CI_REGISTRY_IMAGE}:${CI_COMMIT_REF_SLUG}