Group members flag toggle

What does this MR do and why?

This MR allows us to toggle a feature flag for all the members of a group. This has been a long-requested feature as we're increasingly wanting to toggle flags for GitLab team members or specific user research groups.

You can pass either a single group name or a comma separated list of group names. This will then fetch all the users that are direct members of that group and toggle that flag for them.

Screenshots or screen recordings

Screen_Recording_2022-12-16_at_15.49.15.mov

How to set up and validate locally

1. Set up a group
2. Add members to that group
3. Send a POST request to /api/v4/features/{{flag}} with the group_members param set to the name of that group and a value of true
4. It should enable the flag for all the members in that group

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.