Hide upgrade billing for ramped subscriptions

What does this MR do and why?

Prevents the upgrade button from showing unless the plan allow_upgrade is true. All subscriptions except for ramped ones should still show the button.

Screenshots or screen recordings

Premium Ramp subscription
Premium subscription

How to set up and validate locally

• Run export GITLAB_SIMULATE_SAAS=1
• Restart gdk
• Open your rails console and run ::Gitlab::CurrentSettings.update(check_namespace_plan: true)
• In GL, create a new group with a project
• Purchase CI minutes for the group (cdot/subscriptions/new?plan_id=2c92c0f9699eca030169a2f1f117045f&gl_namespace_id=NAMESPACE_ID)
  • This is to guard against multiple orders incorrectly determining the <code data-sourcepos="19:76-19:88">allow_upgrade</code> value
• Link both a ramped and a non-ramped Premium SaaS subscription to two different groups
• Navigate to groups/GROUP_NAME/-/billings
• Verify that the upgrade button does not show for the group with a ramp subscription
• Verify that the button does show for the other subscription

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

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

Related to #386132 (closed)