add basic gitlab ci yaml

.gitlab-ci.yml

+stages:
+  - deploy
+
+variables:
+  DOCKER_TLS_CERTDIR: ""
+
+deploy_latest:
+  image: docker:20.10.8
+  services:
+    - docker:20.10.8-dind
+  stage: deploy
+  script:
+    - docker login -u "$CI_REGISTRY_USER" -p "$CI_REGISTRY_PASSWORD" "$CI_REGISTRY"
+    - docker build -t $CI_REGISTRY_IMAGE .
+    - docker push $CI_REGISTRY_IMAGE:latest
+  except:
+    - tags
+
+deploy:
+  image: docker:20.10.8
+  services:
+    - docker:20.10.8-dind
+  stage: deploy
+  script:
+    - docker login -u "$CI_REGISTRY_USER" -p "$CI_REGISTRY_PASSWORD" "$CI_REGISTRY"
+    - docker build --cache-from $CI_REGISTRY_IMAGE:latest -t $CI_REGISTRY_IMAGE .
+    - docker push $CI_REGISTRY_IMAGE:$CI_COMMIT_REF_NAME
+  only:
+    - tags