CI: enable new packaging tests using apkg

See `distro/tests/README.md` for more info.

New CI pkg stage tests

    apkg install --build-dep
    apkg test --test-dep

on apkg LXC images using LXC gitlab runner.

A single pkg:make-archive job creates archive shared in all pkg jobs.

A similar change for Knot DNS: knot-dns!1488

See: #612