feat(css): add gl-focus-bg-t-gray-a-08 class

mentioned in commit c1e3e842

mentioned in merge request gitlab-org/frontend/pajamas-adoption-scanner!127 (merged)

mentioned in merge request status-page!745 (merged)

mentioned in merge request gitlab!116201 (closed)

mentioned in merge request gitlab-docs!3727 (closed)

mentioned in merge request gitlab-org/gitlab-services/design.gitlab.com!3332 (merged)

mentioned in merge request gitlab!116736 (merged)

mentioned in merge request gitlab!116885 (merged)

mentioned in merge request gitlab!117076 (merged)

mentioned in merge request gitlab-docs!3751 (merged)