[19.0][ADD] purchase_line_sale_history

[alan196]

task#31940

New module that lets purchasers consult the sales history of a product while filling a purchase order, without leaving the order form.

• Each purchase order line gets a Sales History checkbox; only one line per order can be active at a time (checking one unchecks the rest).
• When active, a year x month pivot table is rendered below the order lines (OWL widget fed by a computed Json field) with the quantities of that product sold in posted customer invoices, credit notes subtracted.
• The history is computed on the exact product variant of the line, so variants of the same template are never mixed.
• The number of past years shown in addition to the current one is configurable in Purchase settings (default: 2).
• Future months of the current year are shown as a dash, distinct from months with zero sales.