[Feature] Add support for Guild Member Flags (#2571)

* implement `GuildUserFlags`

Co-authored-by: Casmir <68127614+csmir@users.noreply.github.com>

src/Discord.Net.WebSocket/Entities/Users/SocketGuildUser.cs

@@ -71,6 +71,8 @@ namespace Discord.WebSocket
         /// <inheritdoc />
         public bool? IsPending { get; private set; }
 
+        /// <inheritdoc />
+        public GuildUserFlags Flags { get; private set; }
 
         /// <inheritdoc />
         public DateTimeOffset? JoinedAt => DateTimeUtils.FromTicks(_joinedAtTicks);
@@ -179,6 +181,8 @@ namespace Discord.WebSocket
                 _timedOutTicks = model.TimedOutUntil.Value?.UtcTicks;
             if (model.Pending.IsSpecified)
                 IsPending = model.Pending.Value;
+
+            Flags = model.Flags;
         }
         internal void Update(ClientState state, PresenceModel model, bool updatePresence)
         {