fix possible bans from Pavel Durov

Core/Extensions/UserExtension.cs

@@ -1,12 +1,17 @@
-using System.Text;
+using System;
+using System.Text;
 using Telegram.Bot.Types;
 
 namespace Kruzya.TelegramBot.Core.Extensions;
 
 public static class UserExtension
 {
+    [Obsolete("Insecure method, currently replaced to dummy text 'Chat Member'")]
     public static string ToHtml(this User user, bool byUsername = false)
     {
+        return "Пользователь";
+
+        /**
         var text = new StringBuilder();
         text.Append($"<a href=\"tg://user?id={user.Id}\">");
            
@@ -19,6 +24,7 @@ public static class UserExtension
             text.Append($"{user.FirstName} {user.LastName}".Trim().HtmlEncode());
         }
         return text.Append("</a>").ToString();
+        */
     }
 
     public static string ToLog(this User user)