Support for round-robin records (one hostname, multiple IP addresses)

[fdcastel]

Both No-Ip and Cloudflare supports round-robin DNS:

• https://www.noip.com/support/knowledgebase/add-txt-record-round-robin-hostname
• https://developers.cloudflare.com/dns/manage-dns-records/how-to/round-robin-dns/

Unfortunately inadyn doesn't have enough information to know what record to update in these cases. The current implementation updates only the first record.

Proposal: to allow hostnames in format hostname@id where id would be

• the label for No-IP provider (e.g. SERVER-1 in this sample from the docs )
• the 32-char id for Cloudflare (e.g. 023e105f4ecef8ad9ca31a8372d0c353 in this sample from the docs )

[troglobit]

Sounds like a great feature. Contributions are welcome!