Update billing page - premium plan header

What does this MR do and why?

Update billing page - premium plan header (for active trials only)

• Adds icons and popovers for each feature item
• DuoChat feature:
  • if the feature is turned on, clicking Explore will open the duo chat
  • if the feature is off, clicking Explore will open duo chat settings
• All Explore links open up the settings to the most recent project
• Update "Choose Premium" CTA to be primary

Pricing table

• Updated the "Choose Premium" CTA in the middle Premium section to a secondary CTA (active trials only) so it does not clash with the primary CTA in the header

Changelog: other

EE: true

References

Screenshots or screen recordings

Before

After: (Active trial only):

Screen Recording 2025-11-10 at 12.15.05 PM.mov

Expired and No Trial Screens (No change):

How to set up and validate locally

• Setup gdk to simulate SaaS - https://docs.gitlab.com/ee/development/ee_features.html#simulate-a-saas-instance and restart GDK
  • Sign out.
• Visit /-/trial_registrations/new. Submit the form / finish registration.
• Log into the rails console to enable subscription / add on purchase:

bin/rails c

Group.last.gitlab_subscription.update(hosted_plan: Plan.find_by(name: 'ultimate_trial'), trial: true, trial_starts_on: 0.days.ago, trial_ends_on: 30.day.from_now)

GitlabSubscriptions::AddOnPurchase.create(subscription_add_on_id: GitlabSubscriptions::AddOn.find_by(name: 'duo_enterprise').id, namespace: Group.last, started_at: 0.days.ago, expires_on: 30.day.from_now, trial: true, quantity: 1, purchase_xid: '1', organization_id: 1)

• Visit /groups/[group-name]/-/billings
  • Observe changes

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Related to #579358