refactor(amavis): move dkim key config to own file

using a seperate file for the DKIM key configuration enables the user
to easily configure with their settings.

MR !4

include/etc/amavis/conf.d/90-dkim

@@ -1,19 +1,3 @@
-dkim_key(
-    'example.org',
-    'dkim',
-    '/certs/amavis/dkim/example.org.dkim.pem'
-);
-
-
-@dkim_signature_options_bysender_maps = (
-    {
-        "example.org" => {
-            d   => 'example.org',
-            a   => 'rsa-sha256',
-            ttl => 10*24*3600
-        }
-    }
-);
 
 $enable_dkim_signing = 1;
 

include/etc/amavis/conf.d/99-dkim-keys

@@ -0,0 +1,18 @@
+dkim_key(
+    'example.org',
+    'dkim',
+    '/certs/amavis/dkim/example.org.dkim.pem'
+);
+
+
+@dkim_signature_options_bysender_maps = (
+    {
+        "example.org" => {
+            s   => 'dkim',
+            d   => 'example.org',
+            a   => 'rsa-sha256',
+            ttl => 10*24*3600
+        }
+    }
+);
+