fix(GlEmptyState): replace Bootstrap CSS utilities with GitLab UI's

mentioned in commit 1e1f8516

mentioned in merge request gitlab!77398 (merged)

mentioned in merge request gitlab-org/gitlab-services/design.gitlab.com!2683 (merged)

mentioned in merge request status-page!439 (merged)

mentioned in merge request status-page!440 (merged)

mentioned in merge request gitlab-docs!2345 (merged)

mentioned in merge request gitlab-docs!2347 (closed)

mentioned in merge request gitlab!77888 (merged)