Add user state to seat-limit audit events

What does this MR do and why?

Adds the affected user's current state to the additional details of the Minimal Access seat-limit audit event. This helps explain why a user was treated as seat-consuming during provisioning.

References

Resolves #631038

Screenshots or screen recordings

Not applicable; this is a backend-only change with no visible UI updates.

How to set up and validate locally

Run bin/rspec ee/spec/lib/gitlab_subscriptions/member_management/seat_aware_provisioning_spec.rb.

Validation completed: 45 examples, 0 failures.

MR acceptance checklist

The change adds one key to the existing free-form audit event details; it does not require a database migration. The focused provisioning specs pass.