Upgrade dependencies for new Langchain + OpenAI API and test interoperability with LiteLLM + Ollama

[snexus]

• Updates the dependencies and underlying backend.
• Breaking changes - split document and model configuration into separate configs.

Addresses the following issues:

• https://github.com/snexus/llm-search/issues/86
• Partially addresses https://github.com/snexus/llm-search/issues/81 - supporting interoperability with other tools via OpenAI API.