I have a Shopify app that creates metafields with a specified namespace but randomly generated keys. I need to read these metafields inside my discount function. However, it seems that Shopify requires knowing the exact key to read a specific metafield, and it can only read one metafield at a time. Is this correct? If so, is there a workaround for reading multiple metafields without knowing their keys? If not, what is the proper method to achieve this?