ci: added docker image building

.gitlab-ci.yml

+docker-image:
+  stage: build
+  image:
+    name: gcr.io/kaniko-project/executor:debug
+    entrypoint: [""]
+  script:
+    - mkdir -p /kaniko/.docker
+    - echo "{\"auths\":{\"${CI_REGISTRY}\":{\"auth\":\"$(printf "%s:%s" "${CI_REGISTRY_USER}" "${CI_REGISTRY_PASSWORD}" | base64 | tr -d '\n')\"}}}" > /kaniko/.docker/config.json
+    - >-
+      /kaniko/executor
+      --context "${CI_PROJECT_DIR}"
+      --dockerfile "${CI_PROJECT_DIR}/Dockerfile"
+      --destination "${CI_REGISTRY_IMAGE}:${CI_COMMIT_TAG}"
+  # rules:
+  #   - if: $CI_COMMIT_TAG
+  #   - master
+
 build-doc:
     image: jupyter/scipy-notebook
     stage: build