gluon-authorized-keys

The gluon-authorized-keys is usually installed to use SSH keys to
authenticate a user against the device. To make this useful, it is also
required to disable passwordless SSH access to the device.

This new dependency is only required when the user doesn't have
gluon-setup-mode enabled already.

Fixes: #1777
Reported-by: yanosz <github@yanosz.net>
Fixes: a753fa79 ("gluon-authorized-keys: add keys from site.conf")
Signed-off-by: Sven Eckelmann <sven@narfation.org>