* Add ability to use virtual environments in local executor
* Copy environment variables from parent environment
* Fix mypy errors and formatting
* Account for venv on Windows
* Use a virtual environment context object instead of path
* Add utility method to create a virtual environment
* Remove assertion using `_venv_path`
* Add tests for `create_virtual_env`
* Modify test code and add output assertion
* Modify test code and assertion
* Execute activation script before actual command on windows
* Add docs for using a virtual env
* Add isort
* Apply isort on py files
* Fix circular import
* Fix format for notebooks
* Fix format
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Co-authored-by: Chi Wang <wang.chi@microsoft.com>