Updated PayPal logic to add region custom field (#3127)

src/Core/Entities/ISubscriber.cs

@@ -13,6 +13,7 @@ public interface ISubscriber
     string SubscriberName();
     string BraintreeCustomerIdPrefix();
     string BraintreeIdField();
+    string BraintreeCloudRegionField();
     string GatewayIdField();
     bool IsUser();
     string SubscriberType();