#21210: feat: add Groq as a cloud provider (#20691)

## Summary - Adds Groq as a full cloud provider for chat completions via its OpenAI-compatible API (`https://api.groq.com/openai/v1`) - Registers 3 models: Llama 3.3 70B (`llama-3.3-70b-versatile`), Mixtral 8x7B (`mixtral-8x7b-32768`), DeepSeek R1 Distill Llama 70B (`deepseek-r1-distill-llama-70b`) - Wires up `GROQ_API_KEY` (already registered in model-auth.ts) for implicit provider resolution and onboarding auth flow Closes #20691 ## Test plan - [x] 4 new unit tests for Groq provider (build, models, implicit resolution, API key resolution) - [x] Updated auth-choice-options e2e test with Groq entry - [x] New auth-choice e2e test for Groq API key onboarding flow - [x] All existing tests pass (nvidia provider, auth-choice options, auth-choice e2e)