Allow to configure pytest-pystack outside the pytests configuration section

**Is your feature request related to a problem? Please describe.**

Option to set parameters to pystack in ini file (`tool.pytest.ini_options` section in `pyproject.toml`) is really nice. But `pytest-pystack` currently could be installed only on linux. So if a project is designed to work on multiple operating systems, then configuring `pytest-pystack` this way collides with `--strict-config`

It will be nice to be able to use strict config and configure `pytest-pystack` in file at the same time.

**Describe the solution you'd like**
A clear and concise description of what you want to happen.

Add option to configure pytest-pystack using own section in pyproject.toml

**Describe alternatives you've considered**

Play with conditional test configuration in tox/nox file.