[feature request] make the freecad model -> urdf converter GUI based

[rydb]

The current FreeCAD model converter as it stands requires hard coding the model files via hard "Model" objects. This will not work for multi part models which need multiple parts to represent one ROS2 link and also would be very tedious to manage for large models with many sub parts.

We need convert the current "export_model_to_urdf.py" to a gui based program, that:

1: can select multiple parts to export as a singular (dae + ROS2 link
2: can let you highlight parts you want to link to each-other, and then select what kind of ros2 link they would be, (continuous, revolution, etc..)
3: comes with a yaml/json/pickle/Model class objects that would represent the object hard coded, etc.. that stores the previous configuration for urdf export so when a user makes a minor change to their model, they don't need to go through the GUI tool every single time.