Dotnet: Add modelServiceId support to SemanticKernelAgent

[cedricmendelin]

The SemanticKernelAgent class has been updated to include an optional modelServiceId parameter, allowing the specification of a service ID for the model.

Why are these changes needed?

Currently, SemanticKernelAgent uses the parameterless method for resolving IChatCompletionSerivce. This will fail, when multiple models are registered in the Kernel.

To support different models registered in the Kernel, I adopted the resolving of the IChatCompletionSerivce within the SemanticKernelAgent with an optional parameter. When it is not set, I resolve the default instance, otherwise, I use the optional parameter as a servide id for resolving the IChatCompletionSerivce service.

Related issue number

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.

[rysweet]

@lokitoth I don't know if ou ported this into agent chat or not but if you did you may want to take this up.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.74%. Comparing base (2a90731) to head (dc5dc9e).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5422   +/-   ##
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  Coverage   78.74%   78.74%           
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  Files         167      167           
  Lines       10025    10025           
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  Hits         7894     7894           
  Misses       2131     2131           

Flag	Coverage Δ
unittests	78.74% <ø> (ø)

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