Avoid apt-key add and just drop the key in /etc/apt/trusted.gpg.d

Only gnupgv is part of the deboostrap set these days, but apt-key needs the full gpg (with gpg-agent) which is just a recommends. Instead just drop the key with an .asc suffix in /etc/apt/trusted.gpg.d which is supported since apt version 1.4

To reproduce add a third party repository as config/archives/foo.list.chroot and config/archives/foo.key.chroot and call lb_config --apt-recommends false so that gpg does not get installed. It's not the prettiest diff, but it was the only way to make it work reliably. Is there another solution?