Finishes files upload process for a given set of entities within property.
This operation is atomic and will either confirm all files or none in case of any failures.

This API is limited to only simple file properties and will not work with any compound types
that require additional processing after upload, like file_collection field itself (you can still confirm files within that collection).

Confirming files with this API in a manual collection will also trigger a recalculation of all depended fields in parent project.
This, together with the fact that multiple files are being confirmed at once aims to reduce token consumption in parent projects.