Added missing billing name for Future Payments (#441)

Addresses the issue found when calling confirmSetupIntent() showing the following error:
> You passed an empty string for 'payment_method_data[billing_details][name]'.

Co-authored-by: Rémon <[email protected]>

Author: cybex-dev

example/lib/screens/others/setup_future_payment_screen.dart

@@ -112,6 +112,7 @@ class _SetupFuturePaymentScreenState extends State<SetupFuturePaymentScreen> {
 
       // 2. Gather customer billing information (ex. email)
       final billingDetails = BillingDetails(
+        name: "Test User",
         email: '[email protected]',
         phone: '+48888000888',
         address: Address(