TODO: Add feet_edge rewards to avoid terrain edge

[giulioturrisi]

This could avoid the robot putting its feet on the edge of stairs etc. Not sure how to do this, some parkour papers implemented it on IsaacGym, there is a version here for Isaaclab https://github.com/CAI23sbP/Isaaclab_Parkour, but never tried.

Not currently working on it, PR are welcome!