[knot-dns-users] Algorithm roll enhancement

I have found a situation where I think the Knot behaviour around algorithm rolls could be better. It's one of those "prevent the user from hurting themselves" situations, in which I would have hurt myself if this had involved anything other than an old, unused zone. :) The suggestion is a simple one: when doing an automated algorithm roll, the KSK submission check should remain negative until the parental DS set exactly matches the set requested by the published CDS set (substitute DNSKEY/CDNSKEY as appropriate). In a situation where CDS scanning is not being done by my parent, I slipped up and only added the new DS record to the parent, leaving the old algorithm's DS record also present. Knot did its submission check, saw the new DS record, and happily continued on with the algorithm roll. This eventually led to a situation that was in violation of RFC 6840 § 5.11 [0]: A signed zone MUST include a DNSKEY for each algorithm present in the zone's DS RRset and expected trust anchors for the zone. I ended up with a situation where I had the new and old DS, but only the new DNSKEY [1]. This seems like a situation that could be avoided by extending the logic of the KSK submission check. In addition to saving users from themselves, it would also help if a situation occurred where the parent had a bug in their CDS processing implementation and failed to remove the old DS. [0]: <https://datatracker.ietf.org/doc/html/rfc6840#section-5.11> [1]: <https://dnsviz.net/d/dns-oarc.org/Yg7ZDw/dnssec/>