lntest: add setup for blinded route forwarding itest

Note: the itest is broken up into multiple commits to make it
more readable, they can be squashed post-review.

itest/list_on_test.go

@@ -558,6 +558,10 @@ var allTestCases = []*lntest.TestCase{
 		Name:     "query blinded route",
 		TestFunc: testQueryBlindedRoutes,
 	},
+	{
+		Name:     "forward blinded",
+		TestFunc: testForwardBlindedRoute,
+	},
 	{
 		Name:     "removetx",
 		TestFunc: testRemoveTx,