debexpo repository multiples issues

This issue is created to list all bugs affecting debexpo repository.

• Missing Packages file when no packages have been uploaded for a distribution/architecture
  This generates errors when running apt update
• No update of the repository state after deleting a package
• No SHA256 field for Packages
  This prevents apt from downloading deb files in buster
• Multiple entries for the Sources and Packages of the same package at the same version (#15 (closed))
• No checksum for .dsc in the Sources.
  This prevent apt source to download the file.

To handle with care: update of the repository upon package deletion can race condition with package importer on repository files. The solution must take that into account.

Bonus round: Create an Release and InRelease file per component/arch and sign it with mentors' key (detached and clearsign).