[IMP] sale_product_matrix: add related field to reduce rpc calls

The matrix configurators makes a rpc call to know if the edited line is 
configurable through matrix or standard configurator.
This rpc can be avoided (and the logic simplified while converting the 
widget to owl) with a related field on the lines.

closes odoo/odoo#100613

Signed-off-by: Victor Feyens (vfe) <vfe@odoo.com>

addons/sale_product_matrix/models/__init__.py

@@ -1,4 +1,5 @@
-# -*- coding: utf-8 -*-
 # Part of Odoo. See LICENSE file for full copyright and licensing details.
-from . import sale_order
+
 from . import product_template
+from . import sale_order
+from . import sale_order_line

addons/sale_product_matrix/models/sale_order_line.py

@@ -0,0 +1,9 @@
+# Part of Odoo. See LICENSE file for full copyright and licensing details.
+
+from odoo import fields, models
+
+
+class SaleOrderLine(models.Model):
+    _inherit = 'sale.order.line'
+
+    product_add_mode = fields.Selection(related='product_template_id.product_add_mode', depends=['product_template_id'])