Merge branch 'Add-user-list-to-feature-flag-api' into 'master'

Add user_list to feature_flag api

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/129899



Merged-by: Andy Soiron <asoiron@gitlab.com>
Approved-by: Sam Figueroa <sfigueroa@gitlab.com>
Approved-by: Costel Maxim <cmaxim@gitlab.com>
Approved-by: Andy Soiron <asoiron@gitlab.com>
Reviewed-by: Andy Soiron <asoiron@gitlab.com>
Reviewed-by: Linjie Zhang <ljzhang@gitlab.cn>
Reviewed-by: Sam Figueroa <sfigueroa@gitlab.com>
Co-authored-by: zhanglinjie <ljzhang@gitlab.cn>