Feature/ab#32299 split openaiservice responsibilities

[jacobwillsmith]

Pull request overview

Simplified the OpenAI configuration resolver to read the normal nested Azure:... keys directly. This removes the explicit compatibility constants and relies on standard .NET configuration binding for environment variables and appsettings values.

Changes:

• Removed the explicit OpenAI env-var compatibility constants from the resolver
• Kept API key and endpoint resolution on the nested Azure:OpenAI:... config keys
• Preserved the legacy Azure:OpenAI:ApiUrl fallback path
• Left the rest of the OpenAI runtime behavior unchanged

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[github-actions]

🧪 Unit Test Results (Parallel Execution)

📊 Summary

Result	Count
✅ Passed	620
❌ Failed	0
⚠️ Skipped	0

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