This commit adds the product tag model.
Purpose
=======
The product tags allows to easily tag given types of product
independently from their category, following their product range, their
seasonal collection, their theme, etc
Specification
=============
A product template takes tags that are valid for all their variants.
In order to add granularity, product variants can also take additionnal
tags.
A field is defined on product variants to allow searching on both
product template and product variant tags.
task-2675384
Part-of: odoo/odoo#79296
Thibault Libioulle
5b64d252d2