Zenoh-pico add ROS2 Unix example using CycloneDDS CDR serializer

[PetervdPerk-NXP]

Adds a UNIX example to communicate with ROS2 using the native ROS2 message definitions.

For serialization we use the CycloneDDS CDR serializer, for now we compile some components separately. But ideally we would have to have do decouple some modules from CycloneDDS i.e. dds_cdrstream.c and turn it into a standalone library that could run also on small RTOS'es (FreeRTOS, Zephyr and more)

To use the UNIX example you've to specify the ROS_DISTRO and it will automatically generated the definitions and serializer to communicate on a ROS2 topic. For more information see https://github.com/NXPHoverGames/zenoh-pico/blob/c6b7f07914871dd3c1436717ee959dc0fb169784/examples/unix/ros2/README.md

Furthermore this PR has a soft dependency to this eclipse-cyclonedds/cyclonedds#1564 PR to avoiding that we compile the complete DDS stack.

[cguimaraes]

Hi @PetervdPerk-NXP
This is a great contribution on ROS2 integration with Zenoh-Pico. It is awesome to see the community experimenting with Zenoh and we really welcome contributions back to the project. Thank you a lot.

I would like to suggest you to move this PR to our repository dedicated to Zenoh-related demos and/or 3rd technology integration (in this case ROS2 and CycloneDDS): https://github.com/eclipse-zenoh/zenoh-demos/
The reason is simple. We would like to keep the repository free of external dependencies as much as possible.
I will keep this PR open until then...

On side note, could you share for what are you using Zenoh (and Zenoh-Pico in specific)? This feedback is important for us to understand the key requirements from our users and to be able to evolve Zenoh towards your needs.
In case you want to engage with the entire team, feel free to drop us a message on our Discord channel: https://discord.gg/2GJ958VuHs

[PetervdPerk-NXP]

Superseded by eclipse-zenoh/zenoh-demos#8