cli: add tailscale dns query (#13368)

Updates tailscale/tailscale#13326

Adds a CLI subcommand to perform DNS queries using the internal DNS forwarder and observe its internals (namely, which upstream resolvers are being used).

Signed-off-by: Andrea Gottardo <andrea@gottardo.me>

client/tailscale/apitype/apitype.go

@@ -4,7 +4,10 @@
 // Package apitype contains types for the Tailscale LocalAPI and control plane API.
 package apitype
 
-import "tailscale.com/tailcfg"
+import (
+	"tailscale.com/tailcfg"
+	"tailscale.com/types/dnstype"
+)
 
 // LocalAPIHost is the Host header value used by the LocalAPI.
 const LocalAPIHost = "local-tailscaled.sock"
@@ -65,3 +68,11 @@ type DNSOSConfig struct {
 	SearchDomains []string
 	MatchDomains  []string
 }
+
+// DNSQueryResponse is the response to a DNS query request sent via LocalAPI.
+type DNSQueryResponse struct {
+	// Bytes is the raw DNS response bytes.
+	Bytes []byte
+	// Resolvers is the list of resolvers that the forwarder deemed able to resolve the query.
+	Resolvers []*dnstype.Resolver
+}