Feature request: add attribute before import

Hello,

In most cases, the setting of attributes seems not so standard, it would be great if it support adding a specific attribute before importing, otherwise, it needs lots of time to edit the product attributes if it is already imported.

Please check the screenshot:

https://image.prntscr.com/image/ajXgmN4qS72U0hmfclQdCA.png

Thanks and have a nice day.