Expose low-discrepancy sequences in Python

Currently, all functionality related to the low discrepancy sequences is only available in [C++](https://esa.github.io/pagmo2/docs/cpp/utils/discrepancy.html). It would be nice to access those sequences from Python as well.

Start with the linked C++ low-discrepancy sequence documentation and trace the existing implementation in the repository. Then inspect how other C++ functionality is exposed through the Python API. Done means the low-discrepancy sequences are accessible from Python with appropriate coverage for the exposed behavior.

Written by the indexing model from the issue text.