Allow multiple distributions in hosted apt repositories

When caching the upstream Debian or Ubuntu apt repositories, the caches contain entries for multiple distributions under metadata/dists, for example (in case of Debian): buster, buster-updates, stretch.

This shows that it is generally possible to host multiple distributions in a single apt repository.

But, OTOH, hosted apt repositories only allow for one single distribution to be specified, which enforces creation of multiple repositories just to support different distributions.

So the request is to add support for multiple distributions to hosted apt repositories, too.