* Before commit "[feat] Extract all keypoints ", one point over
neighborhood_size was processed to be a potential keypoint, this was
reducing the computation time of keypoints extraction

* Now, all points are processed so the computation time can be increased
in case of dense clouds (32/64/128 Lidar sensors)

* So a parameter is added to downsample the input clouds when extracting
the keypoints to speed up the process.

* The downsampling is random

* /!\ This downsampling only speeds up the keypoints extraction step,
the other steps are mostly driven by the maximum number of extracted keypoints