Specify recipient of tool response in harmony example

[Joshua-Chin]

Summary

This PR specifies the assistant as the recipient of the tool message in the OpenAI Harmony code example.

Motivation

Under the Handling tool calls section, it states that:

A tool message has the following format:

<|start|>{toolname} to=assistant<|channel|>commentary<|message|>{output}<|end|>

So in our example above

<|start|>functions.get_current_weather to=assistant<|channel|>commentary<|message|>{"sunny": true, "temperature": 20}<|end|>

The code in its current state does not include the to=assistant text section.