feat(GlDuoChat): promote "/" commands

mentioned in commit 95e2d7cb

mentioned in merge request gitlab!139832 (merged)

mentioned in merge request gitlab-docs!4476 (merged)

mentioned in merge request gitlab-org/gitlab-services/design.gitlab.com!3665 (merged)

mentioned in merge request gitlab-org/frontend/pajamas-adoption-scanner!248 (closed)

mentioned in merge request status-page!891 (merged)

mentioned in merge request gitlab-org/frontend/pajamas-adoption-scanner!249 (merged)

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

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