feature(pu): add pistonball_env, its unittest and qmix config #5210

	# This workflow will check flake style
	# For more information see: https://help.github.com/actions/language-and-framework-guides/using-python-with-github-actions

	name: style

	on: [push, pull_request]

	jobs:
	style:
	runs-on: ubuntu-latest
	strategy:
	matrix:
	python-version: [3.7, 3.8, 3.9]

	steps:
	- uses: actions/checkout@v2
	- name: Set up Python ${{ matrix.python-version }}
	uses: actions/setup-python@v2
	with:
	python-version: ${{ matrix.python-version }}
	- name: code style
	run: \|
	python -m pip install "yapf==0.29.0"
	python -m pip install "flake8<=3.9.2"
	python -m pip install "importlib-metadata<5.0.0"
	make format_test flake_check

Provide feedback