Promotion/sale function

[AXYZE9]

Extra module for homepage.

'sale' table in database:
EAN, priceSale, price, startOn, endOn, shop

Properties of product (ex. numbers of CPU cores) should be inherited from 'products' table by searching for EAN.

If startOn value >= current date&time then REST API should serve it
If endOn value >= current date&time then REST API should not serve it anymore & this promotion should go into separate 'SaleArchive' table for archiving and debugging purposes.