feat: Add chat-slash event and emit on slash commands opened

See merge request gitlab-org/gitlab-ui!4790



Merged-by: Paul Slaughter <pslaughter@gitlab.com>
Approved-by: Angelo Rivera <arivera@gitlab.com>
Approved-by: Elwyn Benson <ebenson@gitlab.com>
Approved-by: Paul Slaughter <pslaughter@gitlab.com>
Reviewed-by: Paul Slaughter <pslaughter@gitlab.com>
Reviewed-by: Jannik Lehmann <jlehmann@gitlab.com>
Reviewed-by: Elwyn Benson <ebenson@gitlab.com>
Co-authored-by: Anna Springfield <aspringfield@gitlab.com>

# [102.2.0](gitlab-org/gitlab-ui@v102.1.6...v102.2.0) (2024-11-14)

### Features

* **DuoChat:** Emit chat-slash event on slash commands opened ([07d8ed60](gitlab-org/gitlab-ui@07d8ed60))