Use a temporary ntp.monogon.dev CNAME instead of pool.ntp.org

We're currently trying to get a vendor zone assigned
(monogon-dev/monogon#72). Meanwhile, use a CNAME pointing
to pool.ntp.org to avoid a freak accident where someone uses
a WIP version of Metropolis to deploy a million plastic routers.

Change-Id: Ib39006c65a23d2df3a1230c28b0b7245b9e3e3c4
Reviewed-on: https://review.monogon.dev/c/monogon/+/320
Reviewed-by: Lorenz Brun <lorenz@monogon.tech>
diff --git a/metropolis/node/core/time/time.go b/metropolis/node/core/time/time.go
index 6c2e906..f57e892 100644
--- a/metropolis/node/core/time/time.go
+++ b/metropolis/node/core/time/time.go
@@ -33,7 +33,7 @@
 func (s *Service) Run(ctx context.Context) error {
 	// TODO(#72): Apply for a NTP pool vendor zone
 	config := strings.Join([]string{
-		"pool pool.ntp.org iburst",
+		"pool ntp.monogon.dev iburst",
 		"bindcmdaddress /",
 		"stratumweight 0.01",
 		"leapsecmode slew",