Greenfield: Improve error message, do not use internal lightning node on store's lightning API

BTCPayServer/JsonHttpException.cs

@@ -0,0 +1,19 @@
+#nullable enable
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Mvc;
+
+namespace BTCPayServer
+{
+    public class JsonHttpException : Exception
+    {
+        public JsonHttpException(IActionResult actionResult)
+        {
+            ActionResult = actionResult;
+        }
+
+        public IActionResult ActionResult { get; }
+    }
+}