[Postfix] Tempfail if Rspamd not available

To protect from spam when rspamd hang or not yet ready to serve requests postfix should reject incoming mail with temp error

data/conf/postfix/main.cf

@@ -27,7 +27,7 @@ maximal_backoff_time = 1800s
 maximal_queue_lifetime = 5d
 delay_warning_time = 4h
 message_size_limit = 104857600
-milter_default_action = accept
+milter_default_action = tempfail
 milter_protocol = 6
 minimal_backoff_time = 300s
 plaintext_reject_code = 550