invoice: add GetInvoices to proto

This call will return a stream of repeated Invoices, in order to submit
monthly audit summaries to accounting, including PDFs and JPK_V7 codes
(ie. GTU and SP codes).

Change-Id: Id9da2952a6358c5c2c737eee08c473c1fbcfbe7d
diff --git a/bgpwtf/invoice/main.go b/bgpwtf/invoice/main.go
index 5133010..ae17dbb 100644
--- a/bgpwtf/invoice/main.go
+++ b/bgpwtf/invoice/main.go
@@ -130,6 +130,10 @@
 	return &pb.SealInvoiceResponse{}, nil
 }
 
+func (s *service) GetInvoices(req *pb.GetInvoicesRequest, srv pb.Invoicer_GetInvoicesServer) error {
+	return status.Error(codes.Unimplemented, "unimplemented")
+}
+
 func init() {
 	flag.Set("logtostderr", "true")
 }