feat: add "nearest.<service>.internal" mode to internal DNS (#159)

* feat: Adding a "nearest.service.local" mode to internal DNS

* Pass listenAddr to internal DNS server (rather than calling into network.MachineIP)

Also adds an exact round-robin via "rr.{service}" mode. Not sure we want that over random or not, though.

* Remove the resolved count and rotating round-robin. "rr.name" mode is now the same as default with random shuffle.

* Add test on nearest internal DNS lookup

* Add docs on internal DNS order modes

internal/machine/machine.go

@@ -430,7 +430,12 @@ func (m *Machine) Run(ctx context.Context) error {
 			}
 
 			dnsResolver := dns.NewClusterResolver(m.store)
-			dnsServer, err := dns.NewServer(m.IP(), dnsResolver, m.config.DNSUpstreams)
+			dnsServer, err := dns.NewServer(
+				m.IP(),
+				m.state.Network.Subnet,
+				dnsResolver,
+				m.config.DNSUpstreams,
+			)
 			if err != nil {
 				return fmt.Errorf("create embedded DNS server: %w", err)
 			}