add docker image build

build image:

  stage: build

  image: docker:latest

  rules:

    - if: $CI_PIPELINE_SOURCE != "merge_request_event" && $CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH

  before_script:

    - echo $CI_REGISTRY_PASSWORD | docker login $CI_REGISTRY -u $CI_REGISTRY_USER --password-stdin

  script:

    - docker build --tag $CI_REGISTRY_IMAGE .

    - docker push $CI_REGISTRY_IMAGE