feat: make MR pipeline the default workflow

# default workflow rules

# default workflow rules: Merge Request pipelines

workflow:

  rules:

    # exclude merge requests

    - if: $CI_MERGE_REQUEST_ID

    # prevent branch pipeline when an MR is open (prefer MR pipeline)

    - if: '$CI_COMMIT_BRANCH && $CI_OPEN_MERGE_REQUESTS'

      when: never

    - when: always