dnsmasq: a resolver tool and event (ADR 0044/0046)

The mesh's resolver is more than config after all. Tools: dnsmasq_names (what
this node answers, from the generated wildcard file) and dnsmasq_resolve (resolve
a name through this node's own resolver — the check that wildcard-resolution
actually answers). Event: it watches the wildcard file and emits
module.dnsmasq.name.added/.removed as machines' names become resolvable here —
DNS having propagated to this node, distinct from the mesh's node.* events.
Typechecks; manifest parses.

modules/dnsmasq/module.json

@@ -7,6 +7,13 @@
   "provides": [
     "wildcard-resolution"
   ],
+  "emits": [
+    "module.dnsmasq.name.added",
+    "module.dnsmasq.name.removed"
+  ],
+  "own-secrets": {
+    "broker": "/var/lib/dnsmasq/broker"
+  },
   "claims": [
     {
       "name": "the-dns-port",