mod_pubsub_serverinfo: Detect existence of pub/sub node Instead of blindly trying to create the pub/sub node to publish items to, a service discovery query is performed to check if node creation is required. Added various bits of warn and debug logging, to give a user better feedback if and why something is failing.

% Prosody log format for lnav

This is a format definition that allows <https://lnav.org/> to better
handle Prosody logs.

Install it using `lnav -i ./prosody.json`