feat: enhance AzureAIChatCompletionClient validation and add unit tests

[ekzhu]

Resolves #5414

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.12%. Comparing base (af5dcc7) to head (47b20d9).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5417      +/-   ##
==========================================
+ Coverage   78.08%   78.12%   +0.04%     
==========================================
  Files         158      158              
  Lines        9576     9579       +3     
==========================================
+ Hits         7477     7484       +7     
+ Misses       2099     2095       -4     

Flag	Coverage Δ
unittests	78.12% <100.00%> (+0.04%)	⬆️

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