lnrpc/invoicesrpc: expose new lookup modifier to LookupInvoiceV2

lnrpc/invoicesrpc/invoices.proto

@@ -142,10 +142,31 @@ message SubscribeSingleInvoiceRequest {
     bytes r_hash = 2;
 }
 
+enum LookupModifier {
+    // The default look up modifier, no look up behavior is changed.
+    DEFAULT = 0;
+
+    /*
+    Indicates that when a look up is done based on a set_id, then only that set
+    of HTLCs related to that set ID should be returned.
+    */
+    HTLC_SET_ONLY = 1;
+
+    /*
+    Indicates that when a look up is done using a payment_addr, then no HTLCs
+    related to the payment_addr should be returned. This is useful when one
+    wants to be able to obtain the set of associated setIDs with a given
+    invoice, then look up the sub-invoices "projected" by that set ID.
+    */
+    HTLC_SET_BLANK = 2;
+}
+
 message LookupInvoiceMsg {
     oneof invoice_ref {
         bytes payment_hash = 1;
         bytes payment_addr = 2;
         bytes set_id = 3;
     }
+
+    LookupModifier lookup_modifier = 4;
 }