In the attachment_upload method, the status in the file metadata to
processing and the malware_detection backend is called. We check in the
media_auth if the status is ready in order to accept the request.
We want to use the malware_detection module from lasuite library. We add
a new setting MALWARE_DETECTION to configure the backend we want to use.
The callback is also added. It removes the file if it is not safe or
change it's status in the metadata to set it as ready.