Add latest gpt-4o model: `gpt-4o-2024-08-06`

[umermansoor]

Why are these changes needed?

The new gpt-4omni model was released recently. This PR adds support for it and gets rid of the warning when trying to use it: [autogen.oai.client: 08-08 15:24:18] {329} WARNING - Model gpt-4o-2024-08-06 is not found. The cost will be 0. In your config_list, add field {"price" : [prompt_price_per_1k, completion_token_price_per_1k]} for customized pricing.

Related issue number

Checks

• [x] 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.
• [x] I've added tests (if relevant) corresponding to the changes introduced in this PR.
• [x] I've made sure all auto checks have passed.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 25.19%. Comparing base (6279247) to head (ad3e4d8). Report is 73 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3329      +/-   ##
==========================================
- Coverage   32.90%   25.19%   -7.71%     
==========================================
  Files          94      103       +9     
  Lines       10235    10898     +663     
  Branches     2193     2485     +292     
==========================================
- Hits         3368     2746     -622     
- Misses       6580     7860    +1280     
- Partials      287      292       +5     

Flag	Coverage Δ
unittests	25.13% <ø> (-7.78%)	:arrow_down:

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