Fix file validation issues that are causing the dropzone functionality to malfunction.

Problem/Motivation

At present, any custom validation leads to a malfunction in the media library, preventing it from accepting additional files due to an issue with the dropzone AJAX callback in the auto_select_handler.

Steps to reproduce

1. Implement custom validation through a file_validation hook or an event subscriber.
2. Add a media field to the relevant entity.
3. Upload a file that triggers the validation process.
4. Attempt to upload a new file that meets the validation criteria.

Proposed resolution

Add a response to handle auto_select_handler callback.

Remaining tasks

User interface changes

API changes

Data model changes