Allow disabling app services auth

[mattgotteiner]

Purpose

• If you want to get an access token to call the chat API, but are using authentication, app services integrated auth makes this more complicated
• Document how to disable app services authentication and request a token that works using DefaultAzureCredential

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)
[ ] Refactoring (no functional changes, no api changes)
[ ] Documentation content changes
[ ] Other... Please describe:

[pamelafox]

Great, I can document this for the evaluation flow as well, assuming it works.