Added OpenAI Manifold pipeline.

[healdgar]

This modification of the Ollama manifold pipeline introduces an OpenAI-based manifold pipeline for handling chat completions using OpenAI's API. The pipeline:

Registers itself as a manifold with a unique identifier (openai_manifold).
Dynamically fetches available OpenAI models from the API on startup and when configuration changes.
Implements a pipe() function that:
Accepts user messages and constructs a valid OpenAI API request.
Removes unsupported fields (e.g., user metadata) before making API calls.
Supports both streaming and non-streaming responses.
Uses requests to interact with OpenAI’s API for chat completions.
This adaptation enables seamless integration of OpenAI’s models into the manifold framework while maintaining compatibility with existing configurations. 🚀