multi: introduce interface for payment database

config_builder.go

@@ -925,9 +925,9 @@ type DatabaseInstances struct {
 	// InvoiceDB is the database that stores information about invoices.
 	InvoiceDB invoices.InvoiceDB
 
-	// KVPaymentsDB is the database that stores all payment related
+	// PaymentsDB is the database that stores all payment related
 	// information.
-	KVPaymentsDB *paymentsdb.KVPaymentsDB
+	PaymentsDB paymentsdb.DB
 
 	// MacaroonDB is the database that stores macaroon root keys.
 	MacaroonDB kvdb.Backend
@@ -1237,7 +1237,7 @@ func (d *DefaultDatabaseBuilder) BuildDatabase(
 
 		return nil, nil, err
 	}
-	dbs.KVPaymentsDB = kvPaymentsDB
+	dbs.PaymentsDB = kvPaymentsDB
 
 	// Wrap the watchtower client DB and make sure we clean up.
 	if cfg.WtClient.Active {