Port front-end part of 9660aa4543 to glitch-soc
[API] This makes use of a new media posting API (/api/v2/media), supporting
background processing of uploaded files. For Pleroma's purposes, this could
be handled the same as /api/v1/media since afaik Pleroma doesn't do any
transcoding.
Signed-off-by: Thibaut Girka <thib@sitedethib.com>