chore: register postgres_params custom pytest.mark

[MasterOdin]

PR registers the custom pytest.mark.postgres_params mark (per pytest docs) so that should no longer see the following warning when running the pgai tests:

=============================================== warnings summary ===============================================
tests/vectorizer/test_vectorizer_cli.py:320
  /Users/mpeveler/code/timescale/pgai/projects/pgai/tests/vectorizer/test_vectorizer_cli.py:320: PytestUnknownMarkWarning: Unknown pytest.mark.postgres_params - 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.postgres_params(load_openai_key=False)

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html

[Askir]

Ah yes I forgot to do that thank you!