Update create AI Agent form to used shared form component

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/145044



Merged-by: Payton Burdette <pburdette@gitlab.com>
Approved-by: Payton Burdette <pburdette@gitlab.com>
Approved-by: Tomas Vik <tvik@gitlab.com>
Reviewed-by: Darby Frey <dfrey@gitlab.com>
Reviewed-by: Payton Burdette <pburdette@gitlab.com>
Co-authored-by: Darby Frey <dfrey@gitlab.com>