third_party/go: pull in node_exporter, add to metropolis rootfs

Change-Id: I5efe5257e7740bf1721f3dd6f130a3c618e33381
Reviewed-on: https://review.monogon.dev/c/monogon/+/1806
Reviewed-by: Leopold Schabel <leo@monogon.tech>
Tested-by: Jenkins CI
diff --git a/metropolis/node/tools.go b/metropolis/node/tools.go
index 9dcb15c..8c8cb42 100644
--- a/metropolis/node/tools.go
+++ b/metropolis/node/tools.go
@@ -11,5 +11,6 @@
 	_ "github.com/coredns/coredns"
 	_ "github.com/go-delve/delve/cmd/dlv"
 	_ "github.com/opencontainers/runc"
+	_ "github.com/prometheus/node_exporter"
 	_ "gvisor.dev/gvisor/runsc"
 )