Implement a MockOpenAI or MockLLM Server for Improved Testing

### Summary
To ensure the robustness and reliability of our langchain project as we introduce new features, it’s imperative to consider implementing a MockOpenAI/LLM server. This would enable us to run comprehensive tests without affecting our actual OpenAI/LLM interactions

### Motivation
As we continue to expand the project's capabilities, there is a growing concern that new additions might inadvertently affect existing functionalities. The introduction of a MockOpenAI server would facilitate a more controlled testing environment, allowing for:

- Isolated testing of new features without dependency on live OpenAI services.
- Cost-effective way to perform extensive testing.
- Early detection of potential issues and conflicts with new code integrations.