Implement RFC 4702/4703 DDNS updates

[leshow]

https://www.rfc-editor.org/rfc/rfc4703

It would be nice if dora supported ddns updates. We could perhaps use a standalone ddns client like kea-dhcp-ddns for this, or use a rust DNS client like trust-dns.

Idea for a dora config structure for ddns:

ddns:
    # if client_updates is set dora will skip any DDNS updates
    # if use_no_update_flag is set, dora will respect the no update flag in the client FQDN option
    # but otherwise send an update
     update: client_updates | use_no_update_flag
     forward:
         - name: "other.example.com."
           key: "foo" # optional
           ip: 1.2.3.4
     reverse:
         - name: "1.16.172.in-addr.arpa."
           key: "foo" # optional
           ip: 1.2.3.4
     tsig_keys:
          - algorithm: hmac-md5 | hmac-sha1 | hmac-sha256 | hmac-sha384 | hmac-sha512
             name: "foo"
             data: <base64 string>

the kea docs are a good resource: https://kea.readthedocs.io/en/kea-2.0.0/arm/ddns.html#

[leshow]

closed in #11