Cleanup FF saas_user_caps

What does this MR do and why?

This implements: https://gitlab.com/gitlab-org/gitlab/-/issues/421693

Here we also fix #438744 (closed)

Group owners can now set a User Cap for their groups in GitLab.com
Users added beyond the limit set will be pendng approval
https://docs.gitlab.com/ee/user/group/manage.html#user-cap-for-groups

Changelog: changed
EE: true

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

N/A

How to set up and validate locally

The feature is globally available.

To run the e2e test locally:

1. For more details check out the readme file
2. cd gitlab-development-kit/gitlab/qa
3. bundle install
   • You might need to comment this line in the Gemlock file to avoid errors
4. QA_GITLAB_URL="<your-gdk-url>" bundle exec rspec qa/specs/features/ee/browser_ui/11_fulfillment/utilization/saas_user_caps_spec.rb
   • You might need to remove the only: { pipeline: %i[staging staging-canary] } to run the tests locally