Add feature test for role promotion management

What does this MR do and why?

Here we're adding a feature test that covers the main user flows for non-billable promotion management

This feature test is based off of the following feedback !171085 (comment 2188133758)

References

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• This implements #462689 (closed)

MR acceptance checklist

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Screenshots or screen recordings

N/A

How to set up and validate locally

1. bundle exec rspec ee/spec/features/users/member_management_spec.rb