Provide Hash for attachments

[Anthony01M]

To avoid requiring us to download the current file, find what the file hash is, delete from our local machine (if already exists in our database), it would be nice to be able know what the attachment hash is from discord directly.
The usage for this would be for security purposes (in case it's not in the database, we'd then need to upload to a malware detector to detect if that file is or isn't one), which honestly is excessive for a lot of us, especially when you are expected to have a lot of message(s) coming from a server which may or may not contain a lot of attachments leading to resource exhaustion sometimes just to confirm that everyone is safe.
this could also come in handy for images (nsfw images) in safe for work channels.