Add AI icon to duo link trigger

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/158353



Merged-by: Jose Ivan Vargas <jvargas@gitlab.com>
Approved-by: Artur Fedorov <afedorov@gitlab.com>
Approved-by: Jose Ivan Vargas <jvargas@gitlab.com>
Co-authored-by: Samantha Ming <sming@gitlab.com>