ROS message parser of types unknown at compile time and run-time

[lucasw]

Follow up #4 (comment) demonstrate that python and C++ (using shapeshifter, possibly ros_msg_parser) message defintions can be had even if the topic type is completely unknown- this must work for plotjuggler to work but make a simple example anyway.

Answer question of where that type is embedded in a ros system- surely every message published doesn't have a copy?

Then make a zenoh demo that demonstrates the same thing, make sure the publisher can publish anything without knowing the type at all- or if extra information is needed make sure it is provided to zenoh (think this is already happening, just point out where here).

Make a custom message, only use it in a private catkin_ws and publish it out using simple python node.

[lucasw]

See what https://github.com/ros2/ros1_bridge does for mapping ros1 types to ros2, copying contents

determine_field_mapping and similar https://github.com/ros2/ros1_bridge/blob/master/ros1_bridge/__init__.py#L547