Package files carry type specific properties like `debian.distribution`,
`debian.component`, `rpm.group` or `alpine.branch` that decide where a
file lives in a registry, but the API never returned them. A client
listing `GET /packages/{owner}/{type}/{name}/{version}/files` could not
tell which distribution or component a file belongs to, or tell apart
same-named files in different ones. Tools copying packages between
instances, like https://gitea.com/gitea/importer, need them to re-upload
a file to the same place.
This adds a `properties` map to `PackageFile`, limited to the properties
that locate a file. Internal ones like the rpm, alpine, arch and conda
metadata or the Debian control file stay hidden, as they can be many MiB
per file.
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
