[IMP] product: find best price for a vendor based on min qty.

Purpose of this task:
Choose a vendor with the minimum price, respecting the quantity
Before commit:
The system was choosing the vendor by sequence,
But if there are any vendor having a different price for the same product,
based on ordered quantity, then the system can't choose the lowest price.
After this commit:
If there are vendors having different price based on the ordered quantity,
then the system will choose the vendor based on the quantity and lowest price.

task-1947351
closes: https://github.com/odoo/odoo/pull/34049

addons/product/models/product.py

@@ -636,10 +636,9 @@ class ProductProduct(models.Model):
                 continue
             if seller.product_id and seller.product_id != self:
                 continue
-
-            res |= seller
-            break
-        return res
+            if not res or res.name == seller.name:
+                res |= seller
+        return res.sorted('price')[:1]
 
     def price_compute(self, price_type, uom=False, currency=False, company=False):
         # TDE FIXME: delegate to template or not ? fields are reencoded here ...