Fix: Correct API key loading from environment variables (closes #10)

[Theigrams]

Description

This pull request addresses an issue where the llm_params.api_key and text_embedding.llm.api_key variables were being incorrectly set to the literal string "<API_KEY>" due to a lack of proper validation after reading the environment variable GRAPHRAG_API_KEY. The issue was identified in lines 56 and 58 of the code. The proposed fix includes adding conditional checks to ensure that if the API keys are set to "<API_KEY>", they are replaced with the correct values from the respective configuration files (llm_config['api_key'] and embeddings_config['llm']['api_key']).

Related Issues

This pull request addresses issue #10.

Proposed Changes

• Added a conditional check for llm_params.api_key to replace "<API_KEY>" with the correct value from llm_config['api_key'].
• Added a conditional check for text_embedding.llm.api_key to replace "<API_KEY>" with the correct value from embeddings_config['llm']['api_key'].
• Added a check to verify if llm_params.api_key or text_embedding.llm.api_key is empty after loading. If either is empty, a ValueError is raised to notify the user.

Checklist

• I have tested these changes locally.
• I have reviewed the code changes.
• I have updated the documentation (if necessary).
• I have added appropriate unit tests (if applicable).

Additional Notes

No additional notes at this time.

[KylinMountain]

Would you mind to add a further check if api_key is empty, then raise an Exception?

[Theigrams]

Would you mind to add a further check if api_key is empty, then raise an Exception?

Thanks for the suggestion! I've added checks to raise a ValueError if the API keys are empty.
Let me know if anything else needs adjustment.

[KylinMountain]

Don't know is it a good idea to raise exception since lots of people use local llm, what's your opinion?