[16.0][ADD] product_variant_change_template

[ChrisOForgeFlow]

This tool allow reassign existing variants to an empty template, this ideal when odoo has template creation as a initial approach, but after some time you decide to combine similar products as a variants belong a template

You should create empty variants with attributes, then you can select variant and change template

When template original empty variants, automatic inactivated by wizard

Restrictions:

• You can't assign if original uom is different of destination uom