The only changes we make to the default are to enable root login via a
password.
While `PasswordAuthentication yes` is the default, let's set it
explicitly to avoid potential issues in the future.
openssh 9.4p1-2 changed /etc/ssh/sshd_config to add support for
drop-in files in /etc/ssh/sshd_config.d/.
Using drop-in files avoids needing to keep up with changes to the
default /etc/ssh/sshd_config.
