[inventory] New stock visibility controls

Maximum stock level displayed

A new "Max visible ATS" parameter lets you limit the available stock level displayed. You may for example decide to define this to 50: any available stock above this value will be displayed as +50. 

This value has no effect on order taking, meaning that buyers will still be able to order up to the available stock.

Stock level visibility in showroom

Stock level visibility in showroom could be controlled globally for buyers and brand users until now thanks to a "Show ATS in showroom" parameter. For more precise control, we have split it into two parameters "Show ATS to buyers" and "Show ATS to users" that let you control visibility separately for buyers and brand users.