rc: allow to stop launch of configd

https://forum.opnsense.org/index.php?topic=5531.0
(cherry picked from commit e5b04016)

src/etc/rc.d/configd

@@ -9,7 +9,9 @@
 
 . /etc/rc.subr
 
-name=configd
+name="configd"
+rcvar="configd_enable"
+: ${configd_enable="YES"}
 pidfile="/var/run/${name}.pid"
 
 start_precmd=configd_prestart