Previous versions of HedgeDoc suffered from the problem
that changing the media backend required manipulation of
the media links in all created notes. We discussed in
#3704 that it's favourable to have an endpoint that
redirects to the image's original URL. When changing the
media backend, the link stays the same but just the
redirect changes.
Signed-off-by: Erik Michelson <github@erik.michelson.eu>
