Allow supply on sale in product by company (multicompany)

Rational

Current sale_supply module add “sale_supply_on_sale” in product but isn’t configurable by company (multicompany)

Proposal

Use MultiValue in supply_on_sale field

Replace to MultiValue sale_supply_on_sale field:

https://bugs.tryton.org/issue8347

I do not think it will follow the general pattern of product’s fields in Tryton. Most of them are straight on the product/template like salable, purchasable, lead time etc.
As most of those fields are just referential data that are duplicated or used in computation on operation records, I do not think we should try to support all cases in standard. The special cases can always be managed with custom module and the supply_on_sale is no exception.