Add duo free access ending alert

What does this MR do and why?

What

Add duo free access ending alert banner

• Adds new duo free access ending alert banner
• Banner visibility shown to users with the following criteria met:
  • group owners
  • existing paid namespaces
  • existing paid namespaces with no active subscription for the duo pro add on
• Alert banner to appear on group page (including subgroups), and projects page
• Only to appear on .com
• Dismissible and dismissed if subscription is purchased
• Primary CTA directs to customers portal
• Secondary CTA launches modal to contact sales
• Feature flagged (duo_free_access_ending_banner)
• Tracking

Why

See https://gitlab.com/gitlab-org/gitlab/-/issues/482067

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.

Screenshots or screen recordings

How to set up and validate locally

1. Simiulate a SaaS instance
2. Enable feature flag duo_free_access_ending_alert
3. Navigate to a group or project that has the following criteria: owner of group, paid (ultimate or premium), and no active add-ons
4. Observe new alert banner
5. Buy now button links to customers dot
6. Contact sales button launches modal/form

Note: User Users::Callout.last.destroy to show the banner/alert again if dismissed

Related to #482067