dns: nsupdate host records to the authoritative server

Replaces the exported-resources -> puppet DNS master zone-file flow with
per-host RFC2136 dynamic updates against the k8s bind-authoritative write
endpoint (198.18.200.9), so the master no longer manages zone files.

- add profiles::dns::updater: assembles the host's records into a concat
  file and runs nsupdate via a systemd .path unit that watches it; the
  dns-update script sends only the delta and deletes removed records
- switch profiles::dns::record to write local concat fragments
  (zone|name|type|ttl|value) instead of exporting to the master
- include profiles::dns::updater from profiles::dns::base (all nodes)
- inert until profiles::dns::updater::key_secret (TSIG) is set in eyaml
- hiera: updater server/key_name/algorithm in common.yaml

site/profiles/manifests/dns/base.pp

@@ -11,9 +11,12 @@ class profiles::dns::base (
   Optional[String] $ns_role = undef,
 ){
 
-  # install bind_utils
+  # install bind_utils (provides nsupdate)
   include bind::updater
 
+  # assemble the host's DNS records and nsupdate them to the authoritative server
+  include profiles::dns::updater
+
   # if ns_role is set, find all hosts matching that enc_role
   $nameserver_array = $ns_role ? {
     undef   => $nameservers,