[VECGEOM-411] Hooking region objects to LogicalVolume
- a mechanism to hook (abitrary) Region) objects to LogicalVolume's
- design allows to develop a region class outside of VecGeom
result of coding sprint with J. Apostolakis, A. Gheta and S. Wenzel
result of coding sprint with J. Apostolakis, A. Gheta and S. Wenzel