cephadm: update smb env to specify writable shared passwd/group files

Update environment for smb containers to specify arguments that sambacc
will use to configure the containers for a split configuration for
users (passwd) and group files. The writable copy will be store in
the samba state dir (/var/lib/samba in the container) and be shared
across the primary and sidecar containers so that configwatch can
pull new users and groups lists from ceph and apply them live.

Signed-off-by: John Mulligan <jmulligan@redhat.com>