Add Duo Enterprise trial alert for group billing page

What does this MR do and why?

Implement group /billings page designs per tier type to account for new Duo Enterprise trial, existing Duo Pro trial, and new combined Ultimate + Duo Enterprise trial offering paths

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

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Plan	Desktop	Mobile
free
premium
ultimate

How to set up and validate locally

bin/rails c

Feature.enable(:duo_enterprise_trials)

• Setup gdk to simulate SaaS - https://docs.gitlab.com/ee/development/ee_features.html#simulate-a-saas-instance and restart GDK.
• Sign out. Visit /users/sign_up.
• Create a new free group. Visit billing page.
• Make sure you can see the Duo Enterprise alert.

bin/rails c

GitlabSubscription.last.update(hosted_plan: Plan.find_by(name: 'premium'))

• Reload. Make sure you can see the Duo Enterprise alert.

bin/rails c

GitlabSubscription.last.update(hosted_plan: Plan.find_by(name: 'ultimate'))

• Reload. Make sure you can see the Duo Enterprise alert.

bin/rails c

GitlabSubscription.last.update(hosted_plan: Plan.find_by(name: 'gold'))

• Reload. Make sure you cannot see the Duo Enterprise alert.

Related to #472087