[AC-1910] Allocate seats to a provider organization (#3936)

* Add endpoint to update a provider organization's seats for consolidated billing.

* Fixed failing tests

src/Api/Billing/Models/ProviderSubscriptionDTO.cs

@@ -27,6 +27,7 @@ public record ProviderSubscriptionDTO(
                     plan.Name,
                     providerPlan.SeatMinimum,
                     providerPlan.PurchasedSeats,
+                    providerPlan.AssignedSeats,
                     cost,
                     cadence);
             });
@@ -43,5 +44,6 @@ public record ProviderPlanDTO(
     string PlanName,
     int SeatMinimum,
     int PurchasedSeats,
+    int AssignedSeats,
     decimal Cost,
     string Cadence);

src/Api/Billing/Models/UpdateProviderOrganizationRequestBody.cs

@@ -0,0 +1,6 @@
+namespace Bit.Api.Billing.Models;
+
+public class UpdateProviderOrganizationRequestBody
+{
+    public int AssignedSeats { get; set; }
+}