Add Continuous Integration test on parsing URDF models

[diegoferigo]

This PR adds a first test in which rod is used to load URDF models from robot-descriptions/robot_descriptions.py and check the read information against robotology/idyntree.

Note that rod has not direct support of URDF, we only support SDF. As a workaround, we expect to find ign sdf|gz sdf installed system-wise, and call sdformat to convert the URDF to SDF before parsing it with rod.

This processing has some side effect. In particular, the URDF model is processed by sdformat and the resulting SDF might differ particularly regarding the lumping logic of links attached through fixed joints.

The test uses iDynTree as ground truth. Similarly, also iDynTree performs link lumping, but it is not 100% compatible with the logic of sdformat. In particular, this PR considers common robot models that work in iDynTree. There are models in which I get the following mismatches:

• Sensor frames of some model do not become frames in idyntree and still show as links.
• When there's a fixed joint + fake link attached to the base link, idyntree lumps the two base frames keeping a different link than sdformat. Therefore, the considered base frame and the removed link converted to frame are flipped.

The models that do not work will possibly get fixed in the future.

The test runs in two different envs:

• Ubuntu 22.04 installing Gazebo Classic from apt and all the rest from PyPI.
• Ubuntu, macOS, and Windows installing all dependencies with conda.

On Windows, the gz sdf command line we use for the URDF to SDF conversion does not work for some reason, the pytest suite is disabled on this OS. cc @traversaro

Windows error

        if cp.returncode != 0:
            msg = f"Failed to find 'sdf' command part of {executable} installation"
           raise RuntimeError(msg)
           RuntimeError: Failed to find 'sdf' command part of C:\Miniconda3\envs\test\Library\bin\gz.BAT installation