* feat(bridge): Support incoming mosquitto bridge connections

The incoming mosquitto bridge connections add 128 to the protocol
version to indicate ras=true and nl=true.

Support for this was added in mqtt-packet with
https://github.com/mqttjs/mqtt-packet/pull/106



Subscriptions from these connections will have ras=true and nl=true

When publishing to these connections, aedes will now
copy the Packet and set retain to false only if ras is not true.

* clarify that Bridge Protocol is supported only for incoming connections

* Respond to some code review comments

* Move the retain flag clearing into the publish function

This allows all callers of subscribe to receive the retain flag
set to false unless explicitly requested by passing rap=true

* Revert previous behaviour change and adjust test

Co-authored-by: Daniel Lando <daniel.sorridi@gmail.com>