[FIX] sale_project: e-commerce delivered_milestones

Steps to reproduce:

Create a Service Product with the Invoicing Policy "Based on Milestones"
publish its eCommerce page.
When logged out, click on "Add to Cart" on the product's eCommerce page.
an error message occurs

Bug:
since this commit[1] "delivered_milestones" is only a valid selection
for users with the group "group_project_milestone"

Fix:
compute the field as sudo to avoid acces error but still only allow
the correct group to manually set that value

opw-3892462

[1]:50ffc33

closes #165123

X-original-commit: c528097
Signed-off-by: Xavier Bol (xbo) <xbo@odoo.com>
Signed-off-by: Walid Hanniche (waha) <waha@odoo.com>

addons/sale_project/models/product.py

@@ -37,7 +37,7 @@ def _selection_service_policy(self):
     project_template_id = fields.Many2one(
         'project.project', 'Project Template', company_dependent=True, copy=True,
         domain="[('company_id', '=', current_company_id)]")
-    service_policy = fields.Selection('_selection_service_policy', string="Service Invoicing Policy", compute='_compute_service_policy', inverse='_inverse_service_policy')
+    service_policy = fields.Selection('_selection_service_policy', string="Service Invoicing Policy", compute_sudo=True, compute='_compute_service_policy', inverse='_inverse_service_policy')
     service_type = fields.Selection(selection_add=[
         ('milestones', 'Project Milestones'),
     ])