AI Gateway [x.x] New AI Provider: Groq

AI Gateway x.x will add Groq as an official LLM provider.

**DoD**
- `ai-gateway.yaml` spec updated at `app/_data/plugins/ai-proxy.yaml`
- New Groq provider subpage, similar to the [[OpenAI provider page](https://developer.konghq.com/ai-gateway/ai-providers/openai/)](https://developer.konghq.com/ai-gateway/ai-providers/openai/)
- Groq tile and icon added to the LLM Providers page
- Configuration examples for AI Proxy and AI Proxy Advanced, chat routes as minimum

**Size:** S

**Person of contact:** TBD with the team

Start with the AI Gateway specification at app/_data/plugins/ai-proxy.yaml and compare the linked OpenAI provider page. Add the Groq provider page, its tile and icon on the LLM Providers page, and AI Proxy and AI Proxy Advanced configuration examples with chat routes at minimum. Done means all listed documentation and configuration updates are present.

Written by the indexing model from the issue text.