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.

lntest/rpc/wallet_kit.go

@@ -254,6 +254,21 @@ func (h *HarnessRPC) BumpFee(
 	return resp
 }
 
+// BumpForceCloseFee makes a RPC call to the node's WalletKitClient and asserts.
+//
+//nolint:lll
+func (h *HarnessRPC) BumpForceCloseFee(
+	req *walletrpc.BumpForceCloseFeeRequest) *walletrpc.BumpForceCloseFeeResponse {
+
+	ctxt, cancel := context.WithTimeout(h.runCtx, DefaultTimeout)
+	defer cancel()
+
+	resp, err := h.WalletKit.BumpForceCloseFee(ctxt, req)
+	h.NoError(err, "BumpForceCloseFee")
+
+	return resp
+}
+
 // ListAccounts makes a RPC call to the node's WalletKitClient and asserts.
 func (h *HarnessRPC) ListAccounts(
 	req *walletrpc.ListAccountsRequest) *walletrpc.ListAccountsResponse {