Add post trial CTAs to GitLab Duo Pro tab on /usage_quotas page

What does this MR do and why?

Related to #467797

Add post-trial experience for namespaces that trialed Duo Pro with free subscription to GitLab Duo Pro tab on /usage_quotas page for Gitlab.com.

Consist of:

• A post trial alert
• Empty state description updates
• CTAs update
• Trackings

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

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Before	After
Tab is not available for free tier

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
• Make sure you have License locally (can be faked here by returning true).
• Create a new group
• Run the following in rails console

GitlabSubscriptions::AddOn.find_or_create_by(name: 'code_suggestions', description: GitlabSubscriptions::AddOn.descriptions[:code_suggestions])
GitlabSubscriptions::AddOnPurchase.create(subscription_add_on_id: GitlabSubscriptions::AddOn.find_by(name: 'code_suggestions').id, namespace: Group.last, organization_id: 1, started_at: 60.days.ago, expires_on: 5.days.ago, trial: true, quantity: 1, purchase_xid: '1')

• Go to /groups//-/usage_quotas#code-suggestions-usage-tab and observe