Fix "The operation is insecure." when trying to register fido2 device.

navigator.credentials.create(); Doesn't accept a port in the "id" parameter. So, when trying to register a fido2 device via WebAuthn throws: "The operation is insecure." on firefox and "The relying party ID is not a registrable domain suffix of, nor equal to the current domain." on Chrome or Edge.
This commit replaces `$_SERVER['HTTP_HOST']` with `$_SERVER['SERVER_NAME']` when initializing `$WebAuthn` which excludes the port to formulate correct requests.
Now Mailcow allows the registration of fido2 devices when running in a non-standard port(eg. 443).

data/web/inc/prerequisites.inc.php

@@ -60,7 +60,7 @@ $tfa = new RobThree\Auth\TwoFactorAuth($OTP_LABEL, 6, 30, 'sha1', $qrprovider);
 
 // FIDO2
 $formats = $GLOBALS['FIDO2_FORMATS'];
-$WebAuthn = new \WebAuthn\WebAuthn('WebAuthn Library', $_SERVER['HTTP_HOST'], $formats);
+$WebAuthn = new \WebAuthn\WebAuthn('WebAuthn Library', $_SERVER['SERVER_NAME'], $formats);
 $WebAuthn->addRootCertificates($_SERVER['DOCUMENT_ROOT'] . '/inc/lib/WebAuthn/rootCertificates/solo.pem');
 $WebAuthn->addRootCertificates($_SERVER['DOCUMENT_ROOT'] . '/inc/lib/WebAuthn/rootCertificates/apple.pem');
 $WebAuthn->addRootCertificates($_SERVER['DOCUMENT_ROOT'] . '/inc/lib/WebAuthn/rootCertificates/nitro.pem');