feat(payment): integrate TwentyCard payment option and enhance checkout flow

- Added a new payment method for TwentyCard in the checkout process, allowing users to select it alongside direct payment options.
- Implemented the logic for processing TwentyCard payments, including user feedback and dialog interactions for payment confirmation.
- Updated the appsettings files to include configuration for the new payment method.
- Enhanced the user interface in the PackagePurchaseDialog to reflect the new payment option and its requirements.

These changes improve the payment flexibility in the checkout process, providing users with additional options for completing their transactions.

src/FrontOffice.Main/Pages/Checkout.razor.cs

@@ -107,6 +107,33 @@ public partial class Checkout
     }
 
     private async Task ProcessPayment()
+        => await StartGatewayPayment(gatewayProvider: null);
+
+    private async Task ProcessTwentyCardPayment()
+    {
+        if (!CanProceedToPayment || _selectedPackage == null)
+        {
+            Snackbar.Add("لطفاً پکیج را انتخاب کنید.", Severity.Warning);
+            return;
+        }
+
+        var options = new DialogOptions
+        {
+            MaxWidth = MaxWidth.Small,
+            FullWidth = true,
+            CloseOnEscapeKey = true,
+            BackdropClick = true
+        };
+
+        var dialog = await DialogService.ShowAsync<Shared.TwentyCardCreditDialog>(
+            string.Empty, options);
+        var result = await dialog.Result;
+        if (result.Canceled) return;
+
+        await StartGatewayPayment(gatewayProvider: "20card");
+    }
+
+    private async Task StartGatewayPayment(string? gatewayProvider)
     {
         if (_isProcessingPayment) return;
 
@@ -120,11 +147,15 @@ public partial class Checkout
 
         try
         {
-            var response = await PackageClient.CustomerPurchasePackageAsync(new CustomerPurchasePackageRequest
+            var request = new CustomerPurchasePackageRequest
             {
                 PackageId = _selectedPackage.Id,
                 PurchaseMethod = PurchaseMethodEnum.PurchaseMethodGateway
-            });
+            };
+            if (!string.IsNullOrWhiteSpace(gatewayProvider))
+                request.GatewayProvider = gatewayProvider;
+
+            var response = await PackageClient.CustomerPurchasePackageAsync(request);
 
             if (!response.Success)
             {