Use prompty to store prompts

[pamelafox]

Purpose

This is an experimental PR to see what it looks like to use Prompty (https://prompty.ai/) to store prompts.

The benefit:

You can see much more of the prompt in one place. You can even theoretically use the VS Code Prompty extension to play with the prompts, and I think that Azure AI Studio will have some support for Prompty files as well now or in the future.

The drawback:

We have to pull messages back out of the rendered prompt, as we then send them to the message builder function to decide how much will fit inside our context window. That's a bit awkward as it involves assuming that [0] is system, [-1] is most recent user message, and [1:-1] are the few shots. I could have also put the chat history in the prompt, but then I couldn't distinguish between few shots and user messages, and I currently treat them differently when truncating conversation history.

Does this introduce a breaking change?

When developers merge from main and run the server, azd up, or azd deploy, will this produce an error?
If you're not sure, try it out on an old environment.

[ ] Yes
[X] No

Does this require changes to learn.microsoft.com docs?

This repository is referenced by this tutorial
which includes deployment, settings and usage instructions. If text or screenshot need to change in the tutorial,
check the box below and notify the tutorial author. A Microsoft employee can do this for you if you're an external contributor.

[ ] Yes
[X] No

Type of change

[ ] Bugfix
[X] Feature
[ ] Code style update (formatting, local variables)
[X] Refactoring (no functional changes, no api changes)
[ ] Documentation content changes
[ ] Other... Please describe:

Code quality checklist

See CONTRIBUTING.md for more details.

• The current tests all pass (python -m pytest).
• I added tests that prove my fix is effective or that my feature works
• I ran python -m pytest --cov to verify 100% coverage of added lines
• I ran python -m mypy to check for type errors
• I either used the pre-commit hooks or ran ruff and black manually on my code.