feat(finance): add daily paid order count

backend/migrations/000047_finance_daily_paid_order_stats.sql

@@ -0,0 +1,9 @@
+-- +goose Up
+
+ALTER TABLE payment_orders
+  ADD KEY idx_payment_orders_biz_status_paid_at_order (biz_type, status, paid_at, order_id);
+
+-- +goose Down
+
+ALTER TABLE payment_orders
+  DROP KEY idx_payment_orders_biz_status_paid_at_order;