modifications for PAHO MQTT version 2.x

[clmcavaney]

Discovered that PAHO MQTT is now version 2.x. It contains some breaking changes. This pull request addresses those breaking changes.

I think I am 99.9% correct on the new calls to on_connect and on_disconnect

Updates based on https://eclipse.dev/paho/files/paho.mqtt.python/html/migrations.html