✨ support for custom API classification field

[ianardee]

Add support for custom API classification field

API builder classification fields were not taken into account, leading to an exception.

Problem was reported by a potential customer.

How Has This Been Tested

Unit tests updated.

Types of changes

• Docs change / refactoring / dependency upgrade
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.

[fharper]

LGTM