feat: Add support for Groq

[cvauclair]

Model Provider Integration Request

Groq provides a high-performance inference platform optimized for large language model (LLM) workloads. Integrating Groq as an LLM provider in Rig will allow users to take advantage of its efficient processing capabilities.

Resources

• Groq Platform Overview: Groq's Official Website
• API Documentation: Groq API Reference

Additional Notes:
Integration will require implementing the CompletionModel trait for Groq's API.