chore: add reviewers to reviewer roulette

What does this merge request do and why?

Related to https://gitlab.com/gitlab-org/ai-powered/ai-framework/team-hq/-/issues/26

There are currently 10 engineers who volunteered to become AI GW reviewers:

www-gitlab-com]$ grep -r 'ai-gateway: reviewer' data/team_members/|wc -l
10

This MR updates roulette to start suggesting also reviewer for AI gateway MRs.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

Merge request checklist

• Tests added for new functionality. If not, please raise an issue to follow up.
• Documentation added/updated, if needed.