Add built-in auth feature

[pamelafox]

Purpose

This PR adds built-in auth feature using the Bicep graph extension.

Does this introduce a breaking change?

[X] Yes - if someone had a public endpoint and pulled, but not a big concern for this template since it's so young.
[ ] No

Pull Request Type

What kind of change does this Pull Request introduce?

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

How to Test

• azd up
• Confirm you must login to app

[achandmsft]

Looks good, merging.