Register markers to avoid pytest warnings

[CoreyEWood]

Previously we'd get a bunch of warnings like this when running tests:

test/integration/test_groundlight.py:373
  /home/ubuntu/ptdev/python-sdk/test/integration/test_groundlight.py:373: PytestUnknownMarkWarning: Unknown pytest.mark.skip_for_edge_endpoint - is this a typo?  You can register custom marks to avoid this warning - for details, see https://docs.pytest.org/en/stable/how-to/mark.html
    @pytest.mark.skip_for_edge_endpoint(reason="The edge-endpoint does not support passing detector metadata.")

According to the docs, unregistered markers will always produce these warnings. By registering our two custom markers, we don't get these warnings anymore.

[brandon-groundlight]

LGTM