replace PubSubClient with arduino mqtt lib

lib/ArduinoMqttClient/library.properties

@@ -0,0 +1,10 @@
+name=ArduinoMqttClient
+version=0.1.6
+author=Arduino
+maintainer=Arduino <info@arduino.cc>
+sentence=[BETA] Allows you to send and receive MQTT messages using Arduino.
+paragraph=
+category=Communication
+url=https://github.com/arduino-libraries/ArduinoMqttClient
+architectures=*
+includes=ArduinoMqttClient.h