Add missing @OrasModel annotation on CredentialHelperResponse

[ThomasVitale]

Description

Add missing @OrasModel annotation on CredentialHelperResponse to allow access when compiled to a GraalVM native executable.

Fixes gh-684

Testing done

Updated tests for for model annotations.

Submitter checklist

• I have read and understood the CONTRIBUTING guide
• I have run mvn license:update-file-header, mvn spotless:apply, pre-commit run -a, mvn clean install before opening the PR

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.28%. Comparing base (8d8a5e6) to head (08f5788).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #685      +/-   ##
============================================
+ Coverage     86.70%   87.28%   +0.58%     
  Complexity      943      943              
============================================
  Files            43       43              
  Lines          2910     2910              
  Branches        364      364              
============================================
+ Hits           2523     2540      +17     
+ Misses          229      212      -17     
  Partials        158      158              

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[jonesbusy]

Thanks! Good catch!