Reduce wait on onboarding page check to avoid long wait

What does this MR do and why?

In some flows we have to onboard a newly created users, in other flows we do not.

In the cases where we do not, our use of has_element? leads to a 10sec wait before returning false.
Let's add the ability to specific a custom wait length here to avoid unnecessary waiting

How to set up and validate locally

    cd /path/to/gdk/gitlab/qa
    bundle exec rspec qa/specs/features/ee/browser_ui/11_fulfillment/purchase/user_registration_billing_spec.rb

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.