Add option to create DKIM-Filter key files without .priv extension

[llucps]

Hi @d00p ,

Following the https://forum.froxlor.org/index.php?/topic/19622-is-dkim-broken-on-latest-froxlor-01022-update-no-key-for-signature/ post. I've been "patching", basically removing the '.priv' extenstion from

$privkey_filename = \Froxlor\FileDir::makeCorrectFile(Settings::Get('dkim.dkim_prefix') . '/dkim' . $domain['dkim_id'] . '.priv');

but it would be great if you could add the option to create the private key files without the ".priv" extension, so it works with dkim-filter.

Thanks!

[llucps]

Thank you! much appreciated.