add index to dispatcher

kamailio/db_scripts/db_kazoo-specific

@@ -67,6 +67,8 @@ CREATE TABLE active_watchers_log (
                cast(substr(attrs, instr(attrs, "idx=")+4, instr(attrs, ";node")-instr(attrs, "idx=")-4) as integer) idx,
                cast(substr(attrs, instr(attrs, "node=")+5) as varchar(50)) node 
     from dispatcher;
+    
+    create unique index if not exists idx_dispatcher_destination on dispatcher(destination);
 
 EOF
 }