Add .gitlab-ci.yml

.gitlab-ci.yml

+stages:
+  - build
+  - build_tag
+  - build_stable
+
+build_latest:
+  stage: build
+  only:
+    - master
+  tags:
+    - docker-image-build
+  script: "" # unused but this line is required by GitLab CI
+
+build_tag:
+  stage: build_tag
+  only:
+    - tags
+  tags:
+    - docker-image-build
+    
+  script: "" # unused but this line is required by GitLab CI
+  
+  variables:
+    TO: ${CI_REGISTRY_IMAGE}:${CI_COMMIT_TAG} # where to push resulting image. Default, the GitLab registry
+    
+
+build_stable:
+  stage: build_stable
+  when: manual
+  only:
+    - tags
+  tags:
+    - docker-image-build
+    
+  script: "" # unused but this line is required by GitLab CI
+  
+  variables:
+    TO: ${CI_REGISTRY_IMAGE}:stable # where to push resulting image. Default, the GitLab registry