Priority configuration for Publishers routes

[JEnoch]

Describe the feature

In case of high traffic with big payloads and high CPU usage for a host, it may happen that some important messages with smaller payloads suffer an extra latency due to the fill of Zenoh transmission queue with big payloads waiting for fragmentation.
In such case, it would be good to have the important messages published on Zenoh with a higher priority. Thus Zenoh will make them overtake the big payloads in the queue, reducing the latency for higher priority messages.

Ideally the solution would be to map the DDS TRANSPORT_PRIORITY QoS to Zenoh Priority.
However, looking at ROS 2 rclpp interface, the TRANSPORT_PRIORITY is not exposed and cannot be set from ROS 2.

Therefore, the simplest solution is to add for the bridge configuration a setting allowing to configure the priority for the Publishers route, in a similar way than the pub_max_frequencies setting.