Fix Websocket OpenApi (#9935)

* Further split inbound and outbound messages

* Fix datatype for inbound start messages

* fixes from review

MediaBrowser.Controller/Net/WebSocketMessages/Inbound/InboundKeepAliveMessage.cs

@@ -0,0 +1,14 @@
+using System.ComponentModel;
+using MediaBrowser.Model.Session;
+
+namespace MediaBrowser.Controller.Net.WebSocketMessages.Inbound;
+
+/// <summary>
+/// Keep alive websocket messages.
+/// </summary>
+public class InboundKeepAliveMessage : InboundWebSocketMessage
+{
+    /// <inheritdoc />
+    [DefaultValue(SessionMessageType.KeepAlive)]
+    public override SessionMessageType MessageType => SessionMessageType.KeepAlive;
+}