multi: add labels to lnd native transactions

Follow up labelling of external transactions with labels for the
transaction types we create within lnd. Since these labels will live
a life of string matching, a version number and rigid format is added
so that string matching is less painful. We start out with channel ID,
where available, and a transaction "type". External labels, added in a
previous PR, are not updated to this new versioned label because they
are not lnd-initiated transactions. Label matching can check this case,
then check for a version number.

watchtower/lookout/punisher.go

@@ -2,6 +2,7 @@ package lookout
 
 import (
 	"github.com/btcsuite/btcd/wire"
+	"github.com/lightningnetwork/lnd/labels"
 )
 
 // PunisherConfig houses the resources required by the Punisher.
@@ -42,7 +43,8 @@ func (p *BreachPunisher) Punish(desc *JusticeDescriptor, quit <-chan struct{}) e
 	log.Infof("Publishing justice transaction for client=%s with txid=%s",
 		desc.SessionInfo.ID, justiceTxn.TxHash())
 
-	err = p.cfg.PublishTx(justiceTxn, "")
+	label := labels.MakeLabel(labels.LabelTypeJusticeTransaction, nil)
+	err = p.cfg.PublishTx(justiceTxn, label)
 	if err != nil {
 		log.Errorf("Unable to publish justice txn for client=%s"+
 			"with breach-txid=%s: %v",