Add `user_cap_reached?` to EE::Group

Merged Etienne Baqué requested to merge 332590-expose-user-cap-calculation into master

What does this MR do?

This is the last MR for this related issue.

Add user_cap_reached? to EE::Group. This method will later be used by group owners to know when the billable member limit has been reached (more in epic description).

This MR also introduces the :saas_user_caps feature flag (which rollout issue is here).

Does this MR meet the acceptance criteria?

Conformity

Availability and Testing

Security

Does this MR contain changes to processing or storing of credentials or tokens, authorization and authentication methods or other items described in the security review guidelines? If not, then delete this Security section.

  • Label as security and @ mention @gitlab-com/gl-security/appsec
  • The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
  • Security reports checked/validated by a reviewer from the AppSec team

Related to #332590 (closed)

Edited by Etienne Baqué