Merge pull request 'Reduce media ID length from 256 to 32' (#216) from miruka/conduit:reduce-mxc-length into master

Reviewed-on: https://git.koesters.xyz/timo/conduit/pulls/216


Reviewed-by: Timo Kösters <timo@koesters.xyz>

Reviewed-on: https://git.koesters.xyz/timo/conduit/pulls/221

It can be enable in the Rocket.toml config or using ROCKET_FEDERATION_ENABLED=true

Most common filesystems limit paths to 255 bytes.
This change brings down the media ID length to be similar to
Synapse servers (25), and makes it possible for clients to
download media with the ID included in the filename.

Reviewed-on: https://git.koesters.xyz/timo/conduit/pulls/211

They are not in the spec and maubot relies on that