Refactor labels (#4179)

* Create new tables

* wip

* wip

* Refactor LegacyLabel

* Remove LabelFactory

* Add migration

* wip

* wip

* Add pull-payment attachment to tx

* Address kukks points

BTCPayServer.Client/Models/LabelData.cs

@@ -1,9 +1,11 @@
+using System;
 using System.Collections.Generic;
 using Newtonsoft.Json;
 using Newtonsoft.Json.Linq;
 
 namespace BTCPayServer.Client.Models
 {
+    [Obsolete]
     public class LabelData
     {
         public string Type { get; set; }