Implement Benchmarks: Stereo Geometry Reco

the high-level angular resolution is already in the poster plot, but that is not all we need for testing geometry reconstruction. What is missing are the following metrics:

• Gamma-ray point-of-origin resolution, which is just angular resolution (done already in the poster plot). However might want this also pre-gamma/hadron-cuts, or a function of trigger multiplicity or telescope type, to help understand why the resolution looks the way it does.
• Gamma-ray PSF asymmetry. In the poster plot, we only have the resolution, but not any study of the PSF's radial (e.g. coma) or cylindrical asymmetries.
• Ground impact-distance resolution (per energy?)
• Ground impact position distribution (per energy?)
• h_max or X_max resolution: note we we have only true_x_max and we reconsruct h_max. To compare them, we need to use the subarray.atmosphere model to transform h_max into X_max (or vice-versa)

Note also that this metric can be applied to several reconstructions: HillasReconstructor, StereoCombiner (from Mono), ImPACT, etc. So the input column name prefix needs to be configurable