Prepare project to use PCL

[pbosetti]

Use FetchContent or other ways, as needed.

[mrcghidelli]

We've installed the PCL in the computer following this link PointCloudLibrary/pcl#4462 to understand which environmental variables are needed. Then we modified the cmakelists.txt. We included them in the skeletonizer3D.cpp and it compiles them, but we have to verify their use in runtime.