lcitool: support custom container images per-arch

Some distro targets (eg Debian) supply separate named container images per-arch. If we use these, it reduces friction when devs have the common container name for the wrong arch.

This is trivially handled by extending the targety yaml to allow arch specific container names to be set.

The Debian 12, 13 and Sid targets are updated to make use of this facility.

Signed-off-by: Daniel P. Berrangé berrange@redhat.com