E2E: Promote Fulfillment Tests to Blocking

What does this MR do and why?

This MR:

• Promotes the test ee/browser_ui/11_fulfillment/license/license_spec.rb to :blocking based on the latest reliable spec report
• Moves ee/browser_ui/11_fulfillment/purchase/user_registration_billing_spec.rb to ee/browser_ui/11_fulfillment/utilization/user_registration_billing_spec.rb, since seat cost management now falls under grouputilization
• Fixes some flakiness in user_registration_billing_spec.rb where a group needs to be created on the instance first in order for the first billable users count to calculate correctly. If this fix proves to be reliable, we will then be able to promote this spec to :blocking in a follow-up MR.

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.

How to set up and validate locally

A passing e2e:package-and-test pipeline in this MR should suffice for these changes.