We have a feature in our CI setup, wherein we can inject certain extra
apt repositories to the build environment

In our case, we usually enable the debian repositories for certain use
cases. But we also need the archive keyring to be able to validate the
authenticity of the extra repository added.

Having the debian-archive-keying package in the package source builder
can be handy, with the only exception that the docker image will be
slightly larger in size.

Signed-off-by: Ritesh Raj Sarraf <ritesh.sarraf@collabora.com>