feat: add LiteLLM integration to support multiple LLM platforms

[devin-ai-integration]

LiteLLM Integration for Multiple LLM Platforms

This PR adds integration with LiteLLM to support multiple LLM platforms through a unified interface.

Features

• Added a new LiteLLMChatCompletions requester class that inherits from LLMAPIRequester
• Created a YAML manifest file for the LiteLLM requester component
• Implemented a demo script to showcase the LiteLLM integration

How to Use

1. Install LiteLLM: pip install litellm
2. Add a new model in the LangBot web UI with the "LiteLLM" requester
3. Configure the model with your API key and provider settings
4. Run the demo script: python demos/litellm_demo.py

Benefits

• Support for 100+ LLM providers through a single interface
• Consistent API format based on OpenAI's API
• Easy configuration through the existing LangBot UI

Testing

The implementation has been tested locally with the demo script.

Link to Devin run: https://app.devin.ai/sessions/50dea523b85046e68d9e8b366e41b134
Requested by: Junyan Qin (Chin) ([email protected])

[devin-ai-integration]

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