various: create a catch-all NRPT rule when "Override local DNS" is enabled on Windows

Without this rule, Windows 8.1 and newer devices issue parallel DNS requests to DNS servers
associated with all network adapters, even when "Override local DNS" is enabled and/or
a Mullvad exit node is being used, resulting in DNS leaks.

This also adds "disable-local-dns-override-via-nrpt" nodeAttr that can be used to disable
the new behavior if needed.

Fixes tailscale/corp#20718

Signed-off-by: Nick Khyl <nickk@tailscale.com>

net/dns/manager_default.go

@@ -6,10 +6,14 @@
 package dns
 
 import (
+	"tailscale.com/control/controlknobs"
 	"tailscale.com/health"
 	"tailscale.com/types/logger"
 )
 
-func NewOSConfigurator(logger.Logf, *health.Tracker, string) (OSConfigurator, error) {
+// NewOSConfigurator creates a new OS configurator.
+//
+// The health tracker and the knobs may be nil and are ignored on this platform.
+func NewOSConfigurator(logger.Logf, *health.Tracker, *controlknobs.Knobs, string) (OSConfigurator, error) {
 	return NewNoopManager()
 }