cli: --json for tailscale dns status|query

This commit adds `--json` output mode to dns debug commands.

It defines structs for the data that is returned from:
`tailscale dns status` and `tailscale dns query <DOMAIN>` and
populates that as it runs the diagnostics.

When all the information is collected, it is serialised to JSON
or string built into an output and returned to the user.

The structs are defined and exported to golang consumers of this command
can use them for unmarshalling.

Updates #13326

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

cmd/tailscaled/depaware-minbox.txt

@@ -54,6 +54,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/cmd/tailscale/cli                              from tailscale.com/cmd/tailscaled
         tailscale.com/cmd/tailscale/cli/ffcomplete                   from tailscale.com/cmd/tailscale/cli
         tailscale.com/cmd/tailscale/cli/ffcomplete/internal          from tailscale.com/cmd/tailscale/cli/ffcomplete
+        tailscale.com/cmd/tailscale/cli/jsonoutput                   from tailscale.com/cmd/tailscale/cli
         tailscale.com/cmd/tailscaled/childproc                       from tailscale.com/cmd/tailscaled
         tailscale.com/control/controlbase                            from tailscale.com/control/controlhttp+
         tailscale.com/control/controlclient                          from tailscale.com/cmd/tailscaled+