ci: use common templates for docker-build, releasing and publishing

.gitlab-ci.yml

 image: python:3.7
 
+include:
+  - project: "open-source/gitlab-templates"
+    ref: "branch/default"
+    file:                                       # the stages are:
+      - "templates/no-duplicate-pipelines.yml"  # no stage
+      - "templates/docker-build.yml"            # test and publish
+      - "templates/release-on-heptapod.yml"     # release
+      - "templates/publish-pypi.yml"            # release
+
 stages:
   - test
   - release
+  - publish
   - deploy
 
 .test:
@@ -36,35 +46,6 @@ yamllint:
   script:
     - tox -e yamllint
 
-image_build:
-  stage: release
-  image:
-    name: gcr.io/kaniko-project/executor:debug
-    entrypoint: [""]
-  script:
-    - echo "{\"auths\":{\"$CI_REGISTRY\":{\"username\":\"$CI_REGISTRY_USER\",\"password\":\"$CI_REGISTRY_PASSWORD\"}}}" > /kaniko/.docker/config.json
-    - /kaniko/executor
-      --context $CI_PROJECT_DIR
-      --dockerfile $CI_PROJECT_DIR/Dockerfile
-      --destination $CI_REGISTRY_IMAGE:$CI_COMMIT_HG_SHORT_SHA
-  rules:
-    - if: '$CI_COMMIT_REF_NAME != "branch/default"'
-
-image_build_latest:
-  stage: release
-  image:
-    name: gcr.io/kaniko-project/executor:debug
-    entrypoint: [""]
-  script:
-    - echo "{\"auths\":{\"$CI_REGISTRY\":{\"username\":\"$CI_REGISTRY_USER\",\"password\":\"$CI_REGISTRY_PASSWORD\"}}}" > /kaniko/.docker/config.json
-    - /kaniko/executor
-      --context $CI_PROJECT_DIR
-      --dockerfile $CI_PROJECT_DIR/Dockerfile
-      --destination $CI_REGISTRY_IMAGE:$CI_COMMIT_HG_SHORT_SHA
-      --destination $CI_REGISTRY_IMAGE:latest
-  rules:
-    - if: '$CI_COMMIT_REF_NAME == "branch/default"'
-
 deploy:
   image:
     name: lachlanevenson/k8s-kubectl:latest