old_price above price. To build a deals page,
page through every product of the channel and keep those offers.
Page through the catalog
GET /v0/channels/{channelId}/products returns up to limit products (at most 200) ordered by
GTIN. Pass next_cursor from a response as cursor to get the next page; it is null on the last one.
Collect the discounts
deals as “−25% at Nordic Pet”, linking to link.