Add vLLM Support for Gemma variants [1B, 4B, 27b]

[MohammedTaherMcW]

Ticket

Link to JIRA Issue

Problem description

Add vLLM Support for Gemma-3-27b-it

What's changed

Added vLLM support for Gemma-3-27b-it in generator_vllm

Checklist

• All post commit CI passes
• Blackhole Post commit CI with demo tests passes (if applicable)
• Model regression CI passes (if applicable)
• Device performance regression CI passes (if applicable)
• (For models and ops writers) Single-card demo tests CI passes (if applicable) See recommended dev flow.
• Galaxy quick CI passes (if applicable)
• TG demo tests, for Llama CI passes, if applicable, because of current Llama work
• (For runtime and ops writers) T3000 unit tests CI passes (if applicable, since this is run on push to main)
• (For models and ops writers) T3000 demo tests CI passes (if applicable, since this is required for release)
• New/Existing tests provide coverage for changes