MT#56627 debian: Pre-Depend on adduser

Take over git commit 929027 from
https://salsa.debian.org/pkg-voip-team/rtpengine.git

Since we're using adduser within ngcp-rtpengine-daemon's
postinst script, we need to make sure to have adduser available.

Change-Id: Ib80794c8a79811d7d890625b8ae5435ca8acc96a

debian/control

@@ -57,6 +57,9 @@ Recommends:
  ngcp-rtpengine-utils,
 Suggests:
  ngcp-system-tools,
+Pre-Depends:
+ adduser,
+ ${misc:Pre-Depends},
 Depends:
  iptables,
  sysvinit-utils (>= 3.05-4~) | lsb-base (>= 3.0-6),