itest: Add itest for bumpclosefeerate rpc.

Add an itest which will bump the close fee rate of an anchor
channel which is force closed without having any HTLCs at stake.

itest/list_on_test.go

@@ -490,6 +490,10 @@ var allTestCases = []*lntest.TestCase{
 		Name:     "bumpfee",
 		TestFunc: testBumpFee,
 	},
+	{
+		Name:     "bumpforceclosefee",
+		TestFunc: testBumpForceCloseFee,
+	},
 	{
 		Name:     "taproot",
 		TestFunc: testTaproot,