Update of OpenAI (and Azure) models and versions

[marklysze]

Why are these changes needed?

A lot of the current tests are using GPT-4 or GPT-3.5-Turbo. These have been superseded by GPT-4o and GPT-4o-mini, which will be more commonly used by users.

This update changes them to the newer versions in the tests, as well as various other places. Additionally, the Azure version has moved along from 2024-02-01 to 2024-08-06, so this updates that as well.

Files will be added progressively to check for issues.

Related issue number

N/A

Checks

• I've included any doc changes needed for https://ag2ai.github.io/ag2/. See https://ag2ai.github.io/ag2/docs/Contribute#documentation to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

[qingyun-wu]

Looks good. Thanks Mark!