Add ldns-signzone like support.

[ximon18]

Currently depends on domain branch multiple-key-signing, see NLnetLabs/domain#418.

• Supports the basic command line arguments zonefile key [key [key]] and the NSEC3 arguments -n, -a, -t, -s and -p.
• Lacks support for all other command line arguments of ldns-signzone:

  -b            use layout in signed zone and print comments DNSSEC records
  -d            used keys are not added to the zone
  -e <date>     expiration date
  -f <file>     output zone to file (default <name>.signed)
  -i <date>     inception date
  -o <domain>   origin for the zone
  -u            set SOA serial to the number of seconds since 1-1-1970
  -v            print version and exit
  -z <[scheme:]hash>    Add ZONEMD resource record
                <scheme> should be "simple" (or 1)
                <hash> should be "sha384" or "sha512" (or 1 or 2)
                this option can be given more than once
  -Z            Allow ZONEMDs to be added without signing
  -A            sign DNSKEY with all keys instead of minimal
  -U            Sign with every unique algorithm in the provided keys
  -E <name>     use <name> as the crypto engine for signing
                This can have a lot of extra options, see the manual page for more info
  -k <algorithm>,<key>  use `key' with `algorithm' from engine as ZSK
  -K <algorithm>,<key>  use `key' with `algorithm' from engine as KSK

• Needs tests.
• Has a known bug where for some reason invoking with KSK then ZSK in that order on the command line produces a zone which fails validation but swapping the order to ZSK then KSK works fine:

$ cargo run -- signzone -n ../domain/test-data/zonefiles/nsd-example.txt /tmp/x/Kexample.com.+015+60019 /tmp/x/Kexample.com.+015+03191 | tee /tmp/t && ldns-verify-zone /tmp/t -V 9
...
Checking: example.com.
Error: Bogus DNSSEC signature for example.com.  DNSKEY
RRSet:
example.com.    86400   IN      DNSKEY  256 3 15 0ZkeiKDxUOeI/45qg2saMEOaWZKpZymNwvl8d5OtLic= ;{id = 3191 (zsk), size = 256b}
example.com.    86400   IN      DNSKEY  257 3 15 Ssh9h2E6uRIX5Rtm9ZRTRL5v5J5YjkQdS+wsnMzhAn4= ;{id = 60019 (ksk), size = 256b}
Signature:
example.com.    86400   IN      RRSIG   DNSKEY 15 2 86400 20241116133433 20241017133433 60019 example.com. FuQPxHTcPRtxRH3IqG1NxFjnxdWZS2SegZe59MFfRaaat7pWgMU/H/LQ2brptMA/ffLlmuSt6ckQDkplhpc9Dg==