Handle :ping_timeout more gracefully?

[roylez]

From time to time, I see :ping_timeout errors after connection is established. I think this could be handled more gracefully without stopping the connection genserv by resetting its state, and going back to connecting stage.

Probably part of the code in Tortoise. Connection.start_link/2 could be moved to a handle_continue or handle_info to make this easier.

[gausby]

I am working on a upgrade that will support MQTT 5, and that will introduce a redesign in the process architecture…I will give it some thoughts when I get back to that work.