feat: add AAD auth to azure search writer

[mhamilton723]

Related Issues/PRs

#xxx

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[mhamilton723]

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Codecov Report

Attention: Patch coverage is 2.85714% with 34 lines in your changes missing coverage. Please review.

Project coverage is 83.09%. Comparing base (6854b5f) to head (4061715).

Files with missing lines	Patch %	Lines
...re/synapse/ml/services/search/AzureSearchAPI.scala	4.16%	23 Missing ⚠️
...azure/synapse/ml/services/search/AzureSearch.scala	0.00%	11 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2285      +/-   ##
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- Coverage   83.70%   83.09%   -0.61%     
==========================================
  Files         327      327              
  Lines       16788    16802      +14     
  Branches     1500     1499       -1     
==========================================
- Hits        14052    13962      -90     
- Misses       2736     2840     +104     

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[mhamilton723]

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[mhamilton723]

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[ranadeepsingh]

Superseded by #2591, which merged to master in 04897ba — closing this out.

Thanks @mhamilton723 — this PR identified the gap and sketched the approach. Rather than modify this branch (which had drifted from master; SearchWriterSuite.scala has since been split into split1/split2), #2591 reimplements the feature on top of the HasAADToken foundation from #1778 and extends it with:

• a single AzureSearchAuth model covering subscription key, AAD token, custom Authorization value, and custom headers;
• one case-insensitive credential-precedence chain shared with the other cognitive services, with the automatic Fabric fallback ranked lowest and evaluated lazily, so a token fetch never runs (or fails) when an explicit credential is present;
• credential validation before any network call, and redaction of auth values from diagnostic output;
• every existing key-based public method preserved, with auth-aware overloads added, so existing user code is unaffected;
• a secret-free AzureSearchAuthSuite plus generic param/header persistence suites.

The user-facing outcome you were after here is in master and ships in the first release after v1.1.3. Please reopen if this branch covered a case that #2591 missed.