Added OpenDKIM to Postfix module

SubModules/postfix/config/opendkim.conf

@@ -0,0 +1,12 @@
+Syslog               yes
+UMask                007
+Socket               local:/var/run/opendkim/opendkim.sock
+PidFile              /var/run/opendkim/opendkim.pid
+OversignHeaders      From
+UserID               opendkim
+Canonicalization     relaxed/simple
+Mode                 s
+KeyTable             refile:/etc/opendkim/KeyTable
+SigningTable         refile:/etc/opendkim/SigningTable
+ExternalIgnoreList   refile:/etc/opendkim/TrustedHosts
+InternalHosts        refile:/etc/opendkim/TrustedHosts