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/Plugins/PointOfSale/Models/UpdatePointOfSaleViewModel.cs

@@ -1,6 +1,7 @@
 using System.Collections.Generic;
 using System.ComponentModel.DataAnnotations;
 using BTCPayServer.Services.Apps;
+using BTCPayServer.Services.Stores;
 using BTCPayServer.Validation;
 using Microsoft.AspNetCore.Mvc.Rendering;
 
@@ -97,7 +98,13 @@ namespace BTCPayServer.Plugins.PointOfSale.Models
         [Display(Name = "Custom CSS Code")]
         public string EmbeddedCSS { get; set; }
         public string Description { get; set; }
+        
         [Display(Name = "Require refund email on checkout")]
         public RequiresRefundEmail RequiresRefundEmail { get; set; } = RequiresRefundEmail.InheritFromStore;
+        
+        [Display(Name = "Request customer data on checkout")]
+        public string CheckoutFormId { get; set; } = GenericFormOption.InheritFromStore.ToString();
+
+        public bool UseNewCheckout { get; set; }
     }
 }