task: #3622735 Add GitLab CI on Drupal 11.4 and PHP 8.4

Closes https://www.drupal.org/project/website_starter/issues/3622735

• Add .gitlab-ci.yml on the drupal.org GitLab templates, with DRUPAL_CORE: 11.4.x-dev and _TARGET_PHP: 8.4.
• Jobs: composer, composer-lint, cspell, and a recipe job that runs drush site:install recipes/website_starter, then checks the default theme is ui_suite_uikit and that nodes were imported.
• PHPCS, PHPStan, PHPUnit, ESLint and Stylelint are skipped: no PHP, CSS or tests. cspell ignores the exported demo content.
• @todo: the composer job takes drupal/webblog from the webblog !4 (merged) branch (Display Builder displays, ~12.0 of webassets and webdev). webblog 12.0.x still requires ~11.0 and installs Layout Builder. Remove the pin once webblog !4 (merged) is merged.
• Overlap with !1 (merged) (Web Dashboard default dashboards, merged): no shared files; webdash, which !1 (merged) adds to recipe.yml, is in the cspell project words.

AI-Generated: Yes

Checkpoints

• File an issue about this project
• Addition/Change/Update/Fix to this project
• Testing to ensure no regression
• Automated unit/functional testing coverage
• Developer Documentation support on feature change/addition
• User Guide Documentation support on feature change/addition
• UX/UI designer responsibilities
• Accessibility and Readability
• Reviewed by a human
• Code review by maintainers
• Full testing and approval
• Credit contributors
• Review with the product owner
• Update Release Notes
• Release