python3-manifest: add statistics subpackage

cpython/Lib/statistics.py contains common statistics functions

"""
Basic statistics module.
This module provides functions for calculating statistics of data, including
averages, variance, and standard deviation.
"""

Signed-off-by: Tim Orling <timothy.t.orling@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>