[Odoo 14] Add product variants to a sale order in bulk

First, you see the default way of adding product variants to a sales order, then I'll show you what settings to enable to enhance this process.

1/ Enable the 'Variant Grid Entry' setting.
2/ Set the 'Sales Variant Selection' to 'Order Grid Entry' on the Variants tab of the product.
3/ Add product variants via a grid to a sales order.