Added unit primitive for generate AI commit message

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/157432



Merged-by: Matthias Käppler <mkaeppler@gitlab.com>
Approved-by: Alex Buijs <abuijs@gitlab.com>
Approved-by: Matthias Käppler <mkaeppler@gitlab.com>
Reviewed-by: Matthias Käppler <mkaeppler@gitlab.com>
Co-authored-by: Phil Hughes <me@iamphill.com>