Feature Request: echo=true in llama-server

[ciaran-regan-ie]

Prerequisites

• [X] I am running the latest code. Mention the version if possible as well.
• [X] I carefully followed the README.md.
• [X] I searched using keywords relevant to my issue to make sure that I am creating a new issue that is not already open (or closed).
• [X] I reviewed the Discussions, and have a new and useful enhancement to share.

Feature Description

The llama-server allows api calls with logprobs=1, but it would be very nice to also include the option to set echo=True, as was available for older OpenAI models such as davinci-002.

Motivation

This would allow for a number of interesting possibilities such as inferring the likelihood of a prompt given a completion, as done in this project.

OpenAI depreciates the echo option because it's too useful :) would be great to have it back in llama.cpp.

Possible Implementation

No response