feat(CSS): add `gl-md-h-9` and `gl-pl-12` utility CSS classes

mentioned in commit 0d466e8f

mentioned in merge request status-page!893 (merged)

mentioned in merge request gitlab!141414 (merged)

mentioned in merge request gitlab-docs!4525 (merged)

mentioned in merge request gitlab-org/gitlab-services/design.gitlab.com!3691 (merged)

mentioned in merge request gitlab-org/frontend/pajamas-adoption-scanner!268 (merged)

mentioned in merge request gitlab-org/frontend/pajamas-adoption-scanner!269 (merged)

mentioned in merge request gitlab-org/frontend/playground/accessibility-scanner!21 (merged)