refactor: consolidate prompt templating to jinja2

What does this merge request do and why?

Closes #601 (closed)

How to set up and validate locally

Make a chat request:

curl -X 'POST' \
   'http://localhost:5052/v2/chat/agent' \
   -H 'accept: application/json' \
   -H 'Content-Type: application/json' \
   -d '{"prompt": "What is your name?",
        "options": {
            "agent_scratchpad": {
                "agent_type": "react",
                "steps": []
            },
            "chat_history": [""]
        }}'

Merge request checklist

• Tests added for new functionality. If not, please raise an issue to follow up.
• Documentation added/updated, if needed.