Add instructions to set up integration testing to contributor docs

[kylediaz]

It looks like the integration tests need these variables set in order to run properly. I didn't see it documented anywhere so I added it to the setup guide.

Also, is my project misconfigured or have the integration tests been broken for a a few weeks now? It looks like they have been broken since this commit, where you add new arguments to the function invalidate_edges, but don't update its uses in test_temporal_operations_int.py.

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[!IMPORTANT] Add environment variable setup instructions for integration tests to CONTRIBUTING.md.

• Documentation:
  • Adds instructions in CONTRIBUTING.md for setting environment variables required for integration tests: TEST_OPENAI_API_KEY, TEST_OPENAI_MODEL, NEO4J_URI, NEO4J_USER, NEO4J_PASSWORD.

^{This description was created by for c97a0666ba8a69f37ae3c7eb8e513e007e1380b1. It will automatically update as commits are pushed.}

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[kylediaz]

I have read the CLA Document and I hereby sign the CLA

[danielchalef]

thanks for contributing, @kylediaz . We're working to fix the int tests.