Use find_namespace_packages to get needed subdirectories to silent lots of warnings

[jcwchen]

Description

Use find_namespace_packages instead of find_packages to silent lots of warnings.

Motivation and Context

Currently there is a lot of warnings about using find_packages by setuptools in CIs. Related discussion: pypa/setuptools#3340.

Warning message is like:

2022-08-24T04:07:24.6253054Z /opt/python/cp38-cp38/lib/python3.8/site-packages/setuptools/command/build_py.py:202: SetuptoolsDeprecationWarning:     Installing 'onnx.backend.test.data.node.test_blackmanwindow.test_data_set_0' as data is deprecated, please list it in `packages`.
2022-08-24T04:07:24.6253649Z     !!
2022-08-24T04:07:24.6253751Z 
2022-08-24T04:07:24.6253758Z 
2022-08-24T04:07:24.6253879Z     ############################
2022-08-24T04:07:24.6254179Z     # Package would be ignored #
2022-08-24T04:07:24.6254472Z     ############################
2022-08-24T04:07:24.6255051Z     Python recognizes 'onnx.backend.test.data.node.test_blackmanwindow.test_data_set_0' as an importable package,
2022-08-24T04:07:24.6255554Z     but it is not listed in the `packages` configuration of setuptools.
2022-08-24T04:07:24.6255793Z 
2022-08-24T04:07:24.6449836Z     'onnx.backend.test.data.node.test_blackmanwindow.test_data_set_0' has been automatically added to the distribution only
2022-08-24T04:07:24.6450376Z     because it may contain data files, but this behavior is likely to change
2022-08-24T04:07:24.6450924Z     in future versions of setuptools (and therefore is considered deprecated).
2022-08-24T04:07:24.6451188Z 
2022-08-24T04:07:24.6638863Z     Please make sure that 'onnx.backend.test.data.node.test_blackmanwindow.test_data_set_0' is included as a package by using
2022-08-24T04:07:24.6639566Z     the `packages` configuration field or the proper discovery methods
2022-08-24T04:07:24.6641711Z     (for example by using `find_namespace_packages(...)`/`find_namespace:`
2022-08-24T04:07:24.6646818Z     instead of `find_packages(...)`/`find:`).
2022-08-24T04:07:24.6647071Z 
2022-08-24T04:07:24.6647296Z     You can read more about "package discovery" and "data files" on setuptools
2022-08-24T04:07:24.6647633Z     documentation page.
2022-08-24T04:07:24.6647874Z 
2022-08-24T04:07:24.6647882Z 
2022-08-24T04:07:24.6647990Z !!