Remove the username from the milter_headers

Rspamd adds the name of the authenticated user by default. Setting add_smtp_user to false prevents the login to be leaked.

core/rspamd/conf/milter_headers.conf

@@ -5,6 +5,9 @@ skip_authenticated = false;
 use = ["x-spamd-bar", "x-spam-level", "x-virus", "authentication-results"];
 
 routines {
+  authentication-results {
+    add_smtp_user = false;
+  }
   x-virus {
     symbols = ["CLAM_VIRUS", "FPROT_VIRUS", "JUST_EICAR"];
   }