[Discounts] Preview (#2772)

* [PHP API] Discounts (#2763)

* [PHP API REF] Added Discount packages

* Generated PHP API for Discounts

* Discount product guide

* Fixed links and navigation

* Removed nav

* Fixed links

* Fixed typo

* Fixed badges

* Removed whitespace

* Fixes before review

* After review fixes

* Currency remark

* Discount migrations (#2768)

* [Discounts] Added migration doc

* Added files

* Update docs/content_management/data_migration/importing_data.md

* Applied suggestions from code review (#2767)

Co-authored-by: julitafalcondusza <[email protected]>

* [Discounts] Search overview (#2773)

* [Discounts] Search overview

* Fixes before review

* Reworded Type sort clause

* Update docs/search/discounts_search_reference/discounts_sort_clauses.md

Co-authored-by: julitafalcondusza <[email protected]>

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Co-authored-by: julitafalcondusza <[email protected]>

* [Discounts] Event reference (#2776)

* [Discounts] Added event reference

* Fixed links

* Fixes before review

* Removed column

* [Discounts] Mentioned discounts in pricing and customer groups (#2775)

* Mentioned discounts in pricing and customer groups

* Before review fixes

* Added mention to the PIM guide

* [Discounts] Discount policies (#2771)

* Permissions

* Build fixes

* Fixed links

* Fixed last links

* Removed link

* Apply suggestions from code review

Co-authored-by: julitafalcondusza <[email protected]>

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Co-authored-by: julitafalcondusza <[email protected]>

* Discounts update (#2774)

* Added update instructions

* Fixed link

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Co-authored-by: julitafalcondusza <[email protected]>

Author: mnocon