Implemented ClientDisconnect event for audio client. (#2520)

src/Discord.Net.WebSocket/API/Voice/ClientDisconnectEvent.cs

@@ -0,0 +1,14 @@
+using Newtonsoft.Json;
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Discord.API.Voice;
+internal class ClientDisconnectEvent
+{
+    [JsonProperty("user_id")]
+    public ulong UserId { get; set; }
+}