Repository access views

Once #755 (closed) is done (and ideally also #756), we'll need a way to serve repositories from the Debusine web application.

MUST: Views to access indexes and packages in an apt-compatible layout

Including possibility to access historical versions of those when they are available
Including views for debian:archive combining multiple debian:suite in a single mirror
Include public keys used to validate the repository in some standard location (perhaps extend Signed-By to include full key material, or provide instructions to clients?)
by-hash
Serve repositories from a separate domain (avoid XSS attacks etc., and it’ll make more sense to apt)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information