Port from azure-ai-inference to openAI package

[pamelafox]

Purpose

This PR ports the backend code to use the openai package, with manually coded token refresh, since many developers would like to know the SDK that they're the most familiar with.

Does this introduce a breaking change?

[ ] Yes
[X] 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

• Deploy
• I need to update the tests back to openai

[achandmsft]

Looks good!