feat(css): Addition of gl-md-flex-direction-column class

mentioned in commit 9c72c503

mentioned in merge request gitlab!78336 (merged)

mentioned in merge request gitlab-org/gitlab-services/design.gitlab.com!2690 (closed)

mentioned in merge request status-page!447 (merged)

mentioned in merge request gitlab-org/gitlab-services/design.gitlab.com!2698 (merged)

mentioned in merge request gitlab-docs!2384 (merged)

mentioned in merge request gitlab-docs!2385 (merged)