[MQTT] - Updates esp_mqtt configuration struct

- Layered config struct
- Fix examples.

examples/protocols/mqtt/ws/main/app_main.c

@@ -107,7 +107,7 @@ static void mqtt_event_handler(void *handler_args, esp_event_base_t base, int32_
 static void mqtt_app_start(void)
 {
     const esp_mqtt_client_config_t mqtt_cfg = {
-        .uri = CONFIG_BROKER_URI,
+        .broker.address.uri = CONFIG_BROKER_URI,
     };
 
     esp_mqtt_client_handle_t client = esp_mqtt_client_init(&mqtt_cfg);