lnwire: add custom records field to type UpdateAddHtlc

- Introduce the field `CustomRecords` to the type `UpdateAddHtlc`.
- Encode and decode the new field into the `ExtraData` field of
  the `update_add_htlc` wire message.

peer/brontide.go

@@ -2193,9 +2193,9 @@ func messageSummary(msg lnwire.Message) string {
 		)
 
 		return fmt.Sprintf("chan_id=%v, id=%v, amt=%v, expiry=%v, "+
-			"hash=%x, blinding_point=%x", msg.ChanID, msg.ID,
-			msg.Amount, msg.Expiry, msg.PaymentHash[:],
-			blindingPoint)
+			"hash=%x, blinding_point=%x, custom_records=%v",
+			msg.ChanID, msg.ID, msg.Amount, msg.Expiry,
+			msg.PaymentHash[:], blindingPoint, msg.CustomRecords)
 
 	case *lnwire.UpdateFailHTLC:
 		return fmt.Sprintf("chan_id=%v, id=%v, reason=%x", msg.ChanID,