Update Azure OpenAI API version to 2024-02-15-preview

[Xtrah]

Why are these changes needed?

On April 2, 2024 the following API preview releases will be retired and will stop accepting API requests:

2023-03-15-preview
2023-06-01-preview
2023-07-01-preview
2023-08-01-preview

To avoid service disruptions, this PR updates to use the latest API version 2024-02-15-preview.

Each individual notebook is not tested, but I did not find any notice of deprecated features or breaking changes.

Related issue number

N/A

Checks

• I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://microsoft.github.io/autogen/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.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (b270a2e) 39.41% compared to head (fdb1a3b) 50.75%.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1692       +/-   ##
===========================================
+ Coverage   39.41%   50.75%   +11.33%     
===========================================
  Files          56       56               
  Lines        5990     5990               
  Branches     1334     1451      +117     
===========================================
+ Hits         2361     3040      +679     
+ Misses       3436     2705      -731     
- Partials      193      245       +52     

Flag	Coverage Δ
unittests	50.66% <100.00%> (+11.25%)	⬆️

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[ekzhu]

Thanks for the PR! It would be great if you can test some of the notebooks locally too make sure they are running correctly with the new API version.