Fix Groq API key format and model references in documentation

[Copilot]

The APPLYWITHLLM_QUICKSTART.md incorrectly showed OpenAI-specific details (API key format, model names) for Groq configuration sections due to copy-paste errors.

Changes

• API key format: Corrected GROQ_API_KEY examples from sk- (OpenAI) to gsk_ (Groq) prefix
• Model references: Replaced GPT models with Groq models (llama-3.3-70b-versatile, mixtral-8x7b-32768)
• Provider support: Updated references to reflect both OpenAI and Groq are supported

Example

Before:

export GROQ_API_KEY="sk-your-key"
export GROQ_MODEL="gpt-4-turbo"

After:

# Option 1: OpenAI
export OPENAI_API_KEY="sk-your-openai-key-here"
export OPENAI_MODEL="gpt-4"  # defaults to gpt-3.5-turbo

# Option 2: Groq
export GROQ_API_KEY="gsk_your-groq-key-here"
export GROQ_MODEL="llama-3.3-70b-versatile"  # defaults to llama-3.3-70b-versatile

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