Revert "Drop the APT GPG key from images that get it via the base container"

This reverts commit 7d4bce20. This change introduces using a keyring from the system path, which requires features which are not (yet) in our packaged version of debos.

This feature is introduced in debos commit d2ab9d3b08056c416bfbcd63c01199e14b2fc3b9

Signed-off-by: Christopher Obbard chris.obbard@collabora.com