consider adding machine-readable `copyright` file (DEP5) file to deb packages

[thaJeztah]

A bit related to the discussion in #1112

Debian introduced a machine-readable format for adding licensing information to packages and it looks like the proposal (https://dep-team.pages.debian.net/deps/dep5/) is accepted and now "1.0". Should we consider adding those?
https://www.debian.org/doc/packaging-manuals/copyright-format/1.0/

Some challenges may be to mark individual files? (i.e. there may be files having a different license).

[thaJeztah]

FWIW; the containerd.io package already has this file, but it looks to be incorrect, as it also includes runc, which is not mentioned in the file;
https://github.com/docker/containerd-packaging/blob/d6a7e6e2f349710e71a409a6cf2527f48b12e864/debian/copyright

[tianon]

See https://salsa.debian.org/go-team/packages/docker/-/blob/487dded61b45c4df44d5b7ec152ef5a4ec4814b3/debian/copyright for a file you can probably borrow/learn a lot from.