rpcserver: attach channel Memo to *lnrpc.Channel struct

This allows us the memo to be returned in responses such as
listchannels.

rpcserver.go

@@ -4224,6 +4224,7 @@ func createRPCOpenChannel(r *rpcServer, dbChannel *channeldb.OpenChannel,
 		PeerScidAlias:         peerScidAlias.ToUint64(),
 		ZeroConf:              dbChannel.IsZeroConf(),
 		ZeroConfConfirmedScid: dbChannel.ZeroConfRealScid().ToUint64(),
+		Memo:                  string(dbChannel.Memo),
 		// TODO: remove the following deprecated fields
 		CsvDelay:             uint32(dbChannel.LocalChanCfg.CsvDelay),
 		LocalChanReserveSat:  int64(dbChannel.LocalChanCfg.ChanReserve),