multi: make canceled invoice garbage collection configurable

This commit extends the application config with a flag to control canceled
invoice garbage collection upon startup.

invoices/invoiceregistry_test.go

@@ -1091,8 +1091,9 @@ func TestOldInvoiceRemovalOnStart(t *testing.T) {
 	require.NoError(t, err)
 
 	cfg := RegistryConfig{
-		FinalCltvRejectDelta: testFinalCltvRejectDelta,
-		Clock:                testClock,
+		FinalCltvRejectDelta:        testFinalCltvRejectDelta,
+		Clock:                       testClock,
+		GcCanceledInvoicesOnStartup: true,
 	}
 
 	expiryWatcher := NewInvoiceExpiryWatcher(cfg.Clock)