Add ability to connect to protected MQTT server

Signed-off-by: Gérondal Thibault <contact@tycale.be>

config.json.sample

@@ -1,5 +1,7 @@
 {
     "host": "localhost",
     "port": 1883,
-    "topic": "tuya/"
-}
+    "topic": "tuya/",
+    "mqtt_user": "",
+    "mqtt_pass": ""
+}

tuya-mqtt.js

@@ -27,7 +27,9 @@ try {
 
 const mqtt_client = mqtt.connect({
     host: CONFIG.host,
-    port: CONFIG.port
+    port: CONFIG.port,
+    username: CONFIG.mqtt_user,
+    password: CONFIG.mqtt_pass,
 });
 
 mqtt_client.on('connect', function (err) {