[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/Core/Billing/Extensions/BillingExtensions.cs

@@ -0,0 +1,9 @@
+using Bit.Core.Enums;
+
+namespace Bit.Core.Billing.Extensions;
+
+public static class BillingExtensions
+{
+    public static bool SupportsConsolidatedBilling(this PlanType planType)
+        => planType is PlanType.TeamsMonthly or PlanType.EnterpriseMonthly;
+}