When migrating from SLE15 to SLE16, if sshd is enabled, warn user about deprecated root password authentication

[fcrozat]

When migrating to SLE16, we should warn users, if sshd is enabled (unless they configured SSHD to not allow root authentication) they might want to enable it back before starting the migration by creating a file
/etc/ssh/sshd_config.d/50-permit-root-login.conf containing:

PermitRootLogin yes

Once the migration is complete, they can install openssh-server-config-rootlogin package and remove the previously added file.