Fixed #16689: re-add note field in API files listing for AssetModel

[r-xyz]

Fixes #16689 reintroducing note field in API files listing for AssetModel.

Also improved the tests, to avoid removal by accident in the future.

[what-the-diff]

PR Summary

• Enhancement of Asset Transformation Method
  The transformAssetModelFile method in the file AssetModelsTransformer.php was modified. This modification now includes a note in the transformed result, enhancing the comprehensive details provided in each asset transformation.

• Update of Test File
  The AssetModelFilesTest.php testing file has been updated. This update not only includes additional tests to confirm proper upload of files annotated with notes, but also improves the assertions to efficiently check the JSON structure. There is also a specific validation process for the note field linked to uploaded files, ensuring its accurate handling.