[FEATURE] Expose geometric information about the robot hand

This can be useful to create simplified models of the robot hand, projections and others. For projections, representation of the state or pose of the end-effector would be necessary.

One idea is to use GPD-like parameters to represent the hand, see e.g [here](https://github.com/atenpas/gpd/blob/master/cfg/hand_geometry.cfg)