ipn/ipnlocal: add tailnet MagicDNS name to ipn.LoginProfile

Start backfilling MagicDNS suffixes on LoginProfiles.

Updates #9286

Signed-off-by: Sonia Appasamy <sonia@tailscale.com>

ipn/ipnlocal/state_test.go

@@ -923,7 +923,7 @@ func TestEditPrefsHasNoKeys(t *testing.T) {
 
 			LegacyFrontendPrivateMachineKey: key.NewMachine(),
 		},
-	}).View())
+	}).View(), "")
 	if p := b.pm.CurrentPrefs().Persist(); !p.Valid() || p.PrivateNodeKey().IsZero() {
 		t.Fatalf("PrivateNodeKey not set")
 	}