[PM-21383] Use Stripe to get provider pricing for display when feature flag is on (#5842)

* Use ProviderPriceAdapter when getting provider subscription

* Update test

src/Core/Billing/Models/ConfiguredProviderPlan.cs

@@ -6,6 +6,7 @@ public record ConfiguredProviderPlan(
     Guid Id,
     Guid ProviderId,
     Plan Plan,
+    decimal Price,
     int SeatMinimum,
     int PurchasedSeats,
     int AssignedSeats);