Pause the catz dbiterator while processing the zone

The dbiterator read-locks the whole zone and it stayed locked during
whole processing time when catz is being read.  Pause the iterator, so
the updates to catz zone are not being blocked while processing the catz
update.

lib/dns/catz.c

@@ -2285,6 +2285,9 @@ dns__catz_update_cb(void *data) {
 			break;
 		}
 
+		result = dns_dbiterator_pause(it);
+		RUNTIME_CHECK(result == ISC_R_SUCCESS);
+
 		if (!is_vers_processed) {
 			/* Keep the version node to skip it later in the loop */
 			vers_node = node;