[Rspamd] Change log level to silent (see docs)

data/conf/rspamd/override.d/logging.inc

@@ -1,4 +1,5 @@
 type = "console";
 systemd = false;
+level = "silent";
 .include "$CONFDIR/logging.inc"
 .include(try=true; priority=20) "$CONFDIR/override.d/logging.custom.inc"