Add native agent support for DeepSeek models and Llama models via Groq

[erik-balfe]

Let's add native agent support (not ReAct) for DeepSeek and Llama models (via Groq) to LlamaIndex. They both now support function calling and are OpenAI API compatible.

• DeepSeek now has function calling: https://platform.deepseek.com/api-docs/function_calling
• Groq offers Llama 3 and 3.1 with function calling (in preview): https://console.groq.com/docs/models#llama-3-groq-70b-tool-use-preview

I'm planning to implement this myself. I'll:

• Develop and test the new agent classes
• Create examples and update the docs