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/Controllers/GreenField/GreenfieldAppsController.cs

@@ -164,6 +164,8 @@ namespace BTCPayServer.Controllers.Greenfield
                 EmbeddedCSS = request.EmbeddedCSS,
                 RedirectAutomatically = request.RedirectAutomatically,
                 RequiresRefundEmail = BoolToRequiresRefundEmail(request.RequiresRefundEmail) ?? RequiresRefundEmail.InheritFromStore,
+                CheckoutFormId = request.CheckoutFormId,
+                CheckoutType = request.CheckoutType ?? CheckoutType.V1
             };
         }