Checkout v2 (#4157)

* Opt-in for new checkout

* Update wording

* Create invoice view update

* Remove jQuery from checkout testing code

* Checkout v2 basics

* WIP

* WIP 2

* Updates and fixes

* Updates

* Design updates

* More design updates

* Cheating and JS fixes

* Use checkout form id whenever invoices get created

* Improve email form handling

* Cleanups

* Payment method exclusion cases for Lightning and LNURL

TODO: Cases and implementation need to be discussed

* Introduce CheckoutType in API and replace UseNewCheckout in backend

Co-authored-by: nicolas.dorier <nicolas.dorier@gmail.com>

BTCPayServer/Models/StoreViewModels/CheckoutAppearanceViewModel.cs

@@ -5,6 +5,7 @@ using System.Linq;
 using BTCPayServer.Services;
 using Microsoft.AspNetCore.Mvc.Rendering;
 using Newtonsoft.Json.Linq;
+using YamlDotNet.Core.Tokens;
 
 namespace BTCPayServer.Models.StoreViewModels
 {
@@ -20,11 +21,21 @@ namespace BTCPayServer.Models.StoreViewModels
             Languages = new SelectList(choices, nameof(chosen.Value), nameof(chosen.Name), chosen);
             DefaultLang = chosen.Value;
         }
+        
         public SelectList Languages { get; set; }
 
+        [Display(Name = "Request customer data on checkout")]
+        public string CheckoutFormId { get; set; }
+
+        [Display(Name = "Include Lightning invoice fallback to on-chain BIP21 payment URL")]
+        public bool OnChainWithLnInvoiceFallback { get; set; }
+
         [Display(Name = "Default payment method on checkout")]
         public string DefaultPaymentMethod { get; set; }
 
+        [Display(Name = "Use the new checkout")]
+        public bool UseNewCheckout { get; set; }
+        
         [Display(Name = "Requires a refund email")]
         public bool RequiresRefundEmail { get; set; }