Discount on discount on mix 40 (RTC-28277)

'Discount on discount' flag is added to Mix 40: "Combine from groups and get a collective discount". Existing price rules have this flag set to 'Editable in offer', and existing offers has this flag unchecked. Field is exported in mix details on promotion offer level.

Improve formatting of ItemSelectionItemImport job logs (RTC-27848)

'ItemSelectionItemImport' job logs in Integration Platform Management are displayed separately for each offer group. Log contains offer group id, time each of job steps took, total time of offer group processing and result: number of items with, and without prices.