websocket: Updated Kconfig to use 'echo.websocket.events' echo server

Updated README to show how to run websocket echo server using Flask

Merges https://github.com/espressif/esp-idf/pull/8262


* Original commit: espressif/esp-idf@23598dfcec

examples/protocols/websocket/main/Kconfig.projbuild

@@ -16,7 +16,7 @@ menu "Example Configuration"
     config WEBSOCKET_URI
         string "Websocket endpoint URI"
         depends on WEBSOCKET_URI_FROM_STRING
-        default "ws://echo.websocket.org"
+        default "ws://echo.websocket.events"
         help
             URL of websocket endpoint this example connects to and sends echo