Ability to preview GitLab Pages in CI

Problem/Motivation

It would be helpful to be able to view rendered documentation in GitLab Pages when reviewing an MR.

Proposed resolution

The approach used by Member Platform: https://git.drupalcode.org/project/member/-/blob/1.0.x/.gitlab-ci.yml?re...

These are the two jobs in the template. We can update the rules so pages build with every MR. Leaving pages deploy job alone

pages:
  stage: deploy
  rules:
    - if: $CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH && $CI_PIPELINE_SOURCE == "push" && $CI_PROJECT_ROOT_NAMESPACE == "project"
      changes:
        - docs/**/*
        - mkdocs.yml
  needs: [Check Code]
  image: python:3.12
  script:
    - pip install mkdocs-material
    - mkdocs build --site-dir public
    - echo "Pages accessible through ${CI_PAGES_URL}"
  artifacts:
    paths:
      - public

pages:
  stage: build
  rules:
    - *skip-pages-rule
    - if: $CI_COMMIT_BRANCH != $CI_DEFAULT_BRANCH
      when: never
    - exists:
        - mkdocs.yml
      when: on_success
  image: python:3.12
  script:
    - cd $CI_PROJECT_DIR && pwd
    - pip install mkdocs-material
    - pwd && ls -l logo* && ls -l docs/logo* || true
    - |
      if [[ -f logo.png ]]; then
        # Do not copy the logo if the destination file already exists.
        test -f docs/logo.png && echo "logo.png not copied to /docs because that file already exists." || cp -v logo.png docs/logo.png
      fi
    - echo "Executing mkdocs build --site-dir public $_MKDOCS_EXTRA"
    - mkdocs build --site-dir public $_MKDOCS_EXTRA
    - printf "$DIVIDER\n* The documentation will be published to the URL $CI_PAGES_URL in the 'pages:deploy' job.$DIVIDER\n"
  artifacts:
    paths:
      - public

Remaining tasks

User interface changes

API changes

Data model changes