Option to force media server and re-upload to destination service if possible

[Wohlstand]

Is your feature request related to a problem? Please describe.
During various tests, I found several problems when uploading content between servers, and other things:

• Several Discord-sent attachments won't each Telegram for some reasons (gets refused by Telegram because of content of URLs treated as errors, etc.)
• Matrix-sent files sometimes gets saved as JSONs with error at the media server.
• Discord-sent stuff as Discord CDN links are inaccessible from China (I have several Chinese users at the Matrix side, and Discord is banned for them).

And I think, to resolve them, it's need to transfer files by different ways, otherwise, they gets missed or inaccessible.

Describe the solution you'd like

• When sending files (such as pictures, videos, etc) via Discord/Telegram, re-upload to Telegram/Matrix/WhatsApp/etc. as files rather than just forward links to them.
• To systems like XMPP/IRC that has no fileshare options except of optional HTTP Upload (when BOSH server is configured), upload to local Media Server rather than just forward Discord's URLs.