System Prompt parameterization

Spice supports defining system prompts for Large Language Models (LLM)s in the spicepod.

Example:

models:
  - name: advice
    from: openai:gpt-4o
    params:
      system_prompt: |
        Write everything in Haiku like a pirate from Australia

More than this, system prompts can use Jinja syntax to allow system prompts to be altered on each v1/chat/completion request. This involves three steps:

1. Add parameterized_prompt: enabled to the model.

2. Use Jinja syntax in the system_prompt parameter for the model in the spicepods.

   models:
    - name: advice
      from: openai:gpt-4o
      params:
        parameterized_prompt: enabled
        system_prompt: |
          Write everything in {{ form }} like a {{ user.character }} from {{ user.country }}

3. Provide the required variables in v1/chat/completion via the .metadata field.

    curl -X POST http://localhost:8090/v1/chat/completions \
      -H "Content-Type: application/json" \
      -d '{
        "model": "advice",
        "messages": [
          {"role": "user", "content": "Where should I visit in San Francisco?"}
        ],
        "metadata": {
          "form": "haiku",
          "user": {
            "character": "pirate",
            "country": "australia"
          }
        }
      }'