[Conf] Add R_DKIM_PERMFAIL to the metric

conf/scores.d/policies_group.conf

@@ -68,6 +68,11 @@ symbols = {
         description = "DKIM verification soft-failed";
         groups = ["dkim"];
     }
+    "R_DKIM_PERMFAIL" {
+        weight = 0.0;
+        description = "DKIM verification hard-failed (invalid)";
+        groups = ["dkim"];
+    }
     "R_DKIM_ALLOW" {
         weight = -0.2;
         description = "DKIM verification succeed";