What's New: Keep-Alive Timeout for WebWSockets: Draft to include

aspnetcore/release-notes/aspnetcore-9/includes/websockets-keep-alive-timeout

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+### Keep-Alive Timeout for WebSockets
+
+The [WebSockets middleware](https://learn.microsoft.com/aspnet/core/fundamentals/websockets#configure-the-middleware) can now be configured for keep alive timeouts.
+
+The keep alive timeout will abort the WebSocket and throw from `WebSocket.ReceiveAsync` if a ping frame from the websocket protocol is sent by the server and the client doesn't reply with a pong frame within the specified timeout. The ping frame is automatically sent by the server and configured with `KeepAliveInterval`. This option is useful when wanting to detect connections that might be slow or ungracefully disconnected.
+
+The keep alive timeout can be configured globally for the WebSocket middleware:
+```csharp
+app.UseWebSockets(new WebSocketOptions { KeepAliveInterval = TimeSpan.FromSeconds(15) });
+```
+
+Or configured per accepted WebSocket:
+```csharp
+app.Run(async (context) =>
+{
+    using var webSocket = await context.WebSockets.AcceptWebSocketAsync(
+        new WebSocketAcceptContext { KeepAliveTimeout = TimeSpan.FromSeconds(15) });
+
+    // ...
+}
+```