itest: add new testCustomChannelsHtlcSuccess itest

Author: Roasbeef

go.mod

@@ -36,6 +36,7 @@ require (
 	github.com/urfave/cli v1.22.9
 	go.etcd.io/bbolt v1.3.11
 	golang.org/x/crypto v0.25.0
+	golang.org/x/exp v0.0.0-20240325151524-a685a6edb6d8
 	golang.org/x/net v0.27.0
 	golang.org/x/sync v0.8.0
 	google.golang.org/grpc v1.65.0
@@ -201,7 +202,6 @@ require (
 	go.uber.org/mock v0.4.0 // indirect
 	go.uber.org/multierr v1.6.0 // indirect
 	go.uber.org/zap v1.23.0 // indirect
-	golang.org/x/exp v0.0.0-20240325151524-a685a6edb6d8 // indirect
 	golang.org/x/mod v0.17.0 // indirect
 	golang.org/x/sys v0.22.0 // indirect
 	golang.org/x/term v0.22.0 // indirect