Configures OpenSSH to read keys from ~/.ssh/authorized_keys.d/* in
addition to authorized_keys, restoring functionality lost when
ssh-key-dir was removed.
Uses 90- prefix to ensure crypto policies and security configs are
applied before user keys are sourced.
Follows the same approach as CoreOS:
https://github.com/coreos/fedora-coreos-config/pull/3885
Signed-off-by: Paul Whalen <pwhalen@fedoraproject.org>
