htlcswitch: add resume modified HTLC action to switch

Introduce `ResumeModified` action to resume standard behavior of a p2p
message with optional modifications as specified by the client during
interception.

intercepted_forward.go

@@ -3,6 +3,7 @@ package lnd
 import (
 	"errors"
 
+	"github.com/lightningnetwork/lnd/fn"
 	"github.com/lightningnetwork/lnd/htlcswitch"
 	"github.com/lightningnetwork/lnd/lntypes"
 	"github.com/lightningnetwork/lnd/lnwire"
@@ -51,6 +52,14 @@ func (f *interceptedForward) Resume() error {
 	return ErrCannotResume
 }
 
+// ResumeModified notifies the intention to resume an existing hold forward with
+// a modified htlc.
+func (f *interceptedForward) ResumeModified(_ fn.Option[lnwire.MilliSatoshi],
+	_ fn.Option[lnwire.CustomRecords]) error {
+
+	return ErrCannotResume
+}
+
 // Fail notifies the intention to fail an existing hold forward with an
 // encrypted failure reason.
 func (f *interceptedForward) Fail(_ []byte) error {