Implement DS record support for ClouDNS

[jamaltebi]

ClouDNS does supprt DS Record ( DS record can be add just for subdomain nor for root domain).

• Question: Can I add a DS record for a subdomain, if there are already other records for the same hostname, such as A, MX, TXT, etc.?

==> Answer: No, you can't. First and foremost, in order for you to be able to add a DS record for your subdomain, the delegation part of your subdomain must be in action. In simple words, the relevant NS records for your subdomain, the "delegators" so to say, must be added first. And to add the NS records, there must be no other records for that particular hostname.

[jamaltebi]

@tlimoncelli I tested the DS record for ClouDNS, It's working. I am waiting for your reply

[IT-Sumpfling]

Perhaps wait with the review. I've just committed some changes which @jamaltebi will test.
These should

• fix the order of NS / DS entries (so no longer necessary to list NS first or to delete in 2 passes)
• implement a very simple rate-limit by delaying each request for 100ms (should fix decrease/delay the number of request per second sended to ClouDNS #1027)
  (ClouDNS seems to rate-limit the API to 10 req/second - but I haven't found a documentation from their side)

[IT-Sumpfling]

This should be fine for now. Another way to only delay after a 429 http status code. Look at providers/desec/protocol.go for an example.

Yes. But I did not yet get around to test if ClouDNS sends 429 or another status code ...

[tlimoncelli]

Yes. But I did not yet get around to test if ClouDNS sends 429 or another status code ...

To be clear: the current solution is sufficient for now.

…

[IT-Sumpfling]

Thank you. Just to be sure - the branch / pull request should be ready for merge from our side.
integration tests run, order of ns/ds does not matter and your review-comments should be addressed.

If you need anything more, let us know.

[tlimoncelli]

Great job!!!