routing: add SubscribeAllPayments to control tower

Add a method 'SubscribeAllPayments' to the control tower, in order to be able to
subscribe to any payment, rather than subscribing to a specific payment hash.

routing/mock_test.go

@@ -557,6 +557,12 @@ func (m *mockControlTowerOld) SubscribePayment(paymentHash lntypes.Hash) (
 	return nil, errors.New("not implemented")
 }
 
+func (m *mockControlTowerOld) SubscribeAllPayments() (
+	*ControlTowerSubscriber, error) {
+
+	return nil, errors.New("not implemented")
+}
+
 type mockPaymentAttemptDispatcher struct {
 	mock.Mock
 
@@ -774,6 +780,13 @@ func (m *mockControlTower) SubscribePayment(paymentHash lntypes.Hash) (
 	return args.Get(0).(*ControlTowerSubscriber), args.Error(1)
 }
 
+func (m *mockControlTower) SubscribeAllPayments() (
+	*ControlTowerSubscriber, error) {
+
+	args := m.Called()
+	return args.Get(0).(*ControlTowerSubscriber), args.Error(1)
+}
+
 type mockLink struct {
 	htlcswitch.ChannelLink
 	bandwidth         lnwire.MilliSatoshi