Add support for desec.io

[vRobM]

Please add support for https://desec.io the modern DDNS service w/ IPv6 support

[YoRyan]

deSEC uses the No-IP protocol, so by setting the endpoint to https://update.dedyn.io, you can technically get DsDDNS to work with that service.

But, here's the rub: If deSEC doesn't receive both the IPv4 and IPv6 addresses in the same update request, it will delete the A or AAAA record that corresponds to the address that wasn't received in that request. DsDDNS doesn't currently support simultaneous updates like this; it requires A and AAAA records to be configured and updated separately, with two separate requests.

So my current thought is to keep the current configuration format, but allow DsDDNS to combine A/AAAA record pairs for the same hostname into single update operations. This would not only allow deSEC to be implemented, but also halve the number of requests for current Google Domains & No-IP users.