Usage of EAN/UPC attribute
It is possible to tell the module the product attribute code, which will hold actual EAN/UPC code.
In Magento store the EAN/UPC attribute should be Global Text type attribute.
Since Single product can have multiple EAN/UPC codes, then they are stored in a single text field.
Codes are separated by comma (,) and all whitespace between them is stripped.
This way when performing a search against single EAN/UPC code, then we can easily use MySQL FIND_IN_SET function to get results.