k0/cockroach: add public DNS entry for cockroach

Change-Id: I934bf348e2165148b515b709e853ab67f039a402
diff --git a/cluster/kube/lib/cockroachdb.libsonnet b/cluster/kube/lib/cockroachdb.libsonnet
index 0b58180..8ebad52 100644
--- a/cluster/kube/lib/cockroachdb.libsonnet
+++ b/cluster/kube/lib/cockroachdb.libsonnet
@@ -53,6 +53,7 @@
 
             namespace: null,
             ownNamespace: cluster.cfg.namespace == null,
+            extraDNS: [],
         },
 
         namespaceName:: if cluster.cfg.namespace != null then cluster.cfg.namespace else name,
@@ -122,7 +123,7 @@
                     ] + [
                         "%s.cluster.local" % s.service.host
                         for s in cluster.servers
-                    ],
+                    ] + cluster.cfg.extraDNS,
                 },
             },