lnwallet: update internal co-op close flow to support musig2 keyspend

In this commit, we update the co-op close flow to support the new musig2
keyspend flow. We'll use some new functional options to allow a caller
to pass in an active musig2 session. If this is present, then we'll use
that to complete the musig2 flow by signing with a partial signature,
and then ultimately combining the signatures at the end.

peer/brontide.go

@@ -2903,6 +2903,7 @@ func (p *Brontide) createChanCloser(channel *lnwallet.LightningChannel,
 	chanCloser := chancloser.NewChanCloser(
 		chancloser.ChanCloseCfg{
 			Channel:      channel,
+			MusigSession: NewMusigChanCloser(channel),
 			FeeEstimator: &chancloser.SimpleCoopFeeEstimator{},
 			BroadcastTx:  p.cfg.Wallet.PublishTransaction,
 			DisableChannel: func(op wire.OutPoint) error {