server: Retrieve prompt template in /props (#8337)

server: Retrieve prompt template in /props (#8337)

* server: Retrieve prompt template in /props

This PR adds the following:
- Expose the model's Jinja2 prompt template from the model in the /props endpoint.
- Change log-level from Error to Warning for warning about template mismatch.

The front-end stands a better chance of actually executing the Jinja template format correctly. Server is currently just guessing it.

Ideally this should have been inside a JSON block that expose the same key/value pairs as listed during startup in "llm_load_print_meta" function.

* Make string buffer dynamic

* Add doc and better string handling

* Using chat_template naming convention

* Use intermediate vector for string assignment