Support translation of documents

@idebr: If you are still interested in the issue, you may provide more information on what should be taken into account.
By means of the documentation, the task of translating documents is related to "real files", which are uploaded to drupal.
I'm not sure, if this is even possible within tmgmt.

My project requirement is pretty basic:
- Upload a file in a node
- Automatically translate the file when translating the node using Deepl

This is supported by tmgmt, see ✨ Translate files / attachments Fixed

The priority for automatic translations for documents in my project has been lowered, so I don't expect to do any development on this feature in the short term