mgr/smb: add a new tls credential resource type

mgr/smb: add a new tls credential resource type

Add a new TLS credential resource type that can currently store one
TLS certificate, TLS key, or TLS CA certificate. This is a new top-level
resource so that they can be use across clusters or managed
independently by different people and or private information can be kept
out a cluster resource stored in a file committed somewhere.

Signed-off-by: John Mulligan <jmulligan@redhat.com>
(cherry picked from commit 173b538c2b520867dc2103be4ff91a66f0cbf76f)