Automatically register `flaky` mark

At [scikit-fingerprints](https://github.com/scikit-fingerprints/scikit-fingerprints), we use `@pytest.mark.flaky` mark quite extensively. To avoid warnings `PytestUnknownMarkWarning: Unknown pytest.mark.flaky`, one needs to [register it in pyproject.toml](https://docs.pytest.org/en/stable/how-to/mark.html) manually. Would it be possible to be registered upon import / usage of `pytest-rerunfailures`? I.e. could the usage of library automatically register its own mark?