Check DuoPro trial eligibility by querying CustomerDot and Zuora

The following discussion from !9454 should be addressed:

To assess the idea in comment https://gitlab.com/gitlab-org/customers-gitlab-com/-/merge_requests/9454#note_1800175885

More discussions https://gitlab.com/gitlab-org/customers-gitlab-com/-/merge_requests/9454#note_1800770447

• @qzhaogitlab started a discussion: (+3 comments)

  To reviewer: we choose to get the namespace's GitlabSubscriptions::AddOnPurchase record from Gitlab. Because:

  • we never delete (we could deprovision by updating the expires_on date though) GitlabSubscriptions::AddOnPurchase record in Gitlab. So the existence of such a record reflects whether the namespace have ever purchased(or trialed) the DuoPro. So this approach is accurate.
  • it is not easy to check the expired paid packs from CustomersDot database. Because when a subscription is deprovisioned, the order's subscription_id will be nullified.