Improve docs on STOMP / WebSocket frame max size

Issue: SPR-17514

src/docs/asciidoc/web/websocket.adoc

@@ -1133,6 +1133,42 @@ application.
 
 
 
+[[websocket-stomp-server-config]]
+=== WebSocket Server
+
+To configure the underlying WebSocket server, the information in
+<<websocket-server-runtime-configuration>> applies. For Jetty, however you need to set
+the `HandshakeHandler` and `WebSocketPolicy` through the `StompEndpointRegistry`:
+
+====
+[source,java,indent=0]
+[subs="verbatim,quotes"]
+----
+	@Configuration
+	@EnableWebSocketMessageBroker
+	public class WebSocketConfig implements WebSocketMessageBrokerConfigurer {
+
+		@Override
+		public void registerStompEndpoints(StompEndpointRegistry registry) {
+			registry.addEndpoint("/portfolio").setHandshakeHandler(handshakeHandler());
+		}
+
+		@Bean
+		public DefaultHandshakeHandler handshakeHandler() {
+
+			WebSocketPolicy policy = new WebSocketPolicy(WebSocketBehavior.SERVER);
+			policy.setInputBufferSize(8192);
+			policy.setIdleTimeout(600000);
+
+			return new DefaultHandshakeHandler(
+					new JettyRequestUpgradeStrategy(new WebSocketServerFactory(policy)));
+		}
+	}
+----
+====
+
+
+
 [[websocket-stomp-message-flow]]
 === Flow of Messages