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.Data/Data/WalletTransactionData.cs

@@ -1,7 +1,9 @@
+using System;
 using Microsoft.EntityFrameworkCore;
 
 namespace BTCPayServer.Data
 {
+    [Obsolete]
     public class WalletTransactionData
     {
         public string WalletDataId { get; set; }