Add simulation of GET endpoint /products to shop.go

[kshpdr]

Task description
Even though it's intended to use shop.go as a client used by shops and they have to implement GET endpoint /products somewhere, now we would probably need it for testing since we don't know when other team is gonna get it running on the one of two shops there and in our case it's really easy to implement.

Tasks
Implement one GET endpoint /products that is going to return list of products according to our Architecture document. Dummy products could be saved in external file products.js and then just extracted from there.

[kshpdr]

Closed since intergrating Hub into shops.