jigasi: set DOMAIN_BASE for SIP account

Fixes: https://github.com/jitsi/docker-jitsi-meet/issues/33

jigasi/rootfs/defaults/sip-communicator.properties

@@ -45,6 +45,7 @@ net.java.sip.communicator.impl.protocol.sip.acc1.Encodings.speex/8000=0
 net.java.sip.communicator.impl.protocol.sip.acc1.Encodings.telephone-event/8000=1
 net.java.sip.communicator.impl.protocol.sip.acc1.Encodings.ulpfec/90000=0
 net.java.sip.communicator.impl.protocol.sip.acc1.OVERRIDE_ENCODINGS=true
+net.java.sip.communicator.impl.protocol.sip.acc1.DOMAIN_BASE={{ .Env.XMPP_DOMAIN }}
 
 # XMPP account used for control
 net.java.sip.communicator.impl.protocol.jabber.acc1=acc1