[FIX] point_of_sale: allow classic users to load demo products

While click on add demo data wizard button it will generate trackback.

Steps to Produce:-
- Create database without demo data.
- Login as Admin.
- Install 'point of sale' module.
- Delete all product
- Create New User and give user access to 'point of sale'.
- Login with new created user.
- Go to 'Point of Sale' module.
- Open new session
- Click on Generate Demo Data >> Error occur

Error: A traceback appears: AccessError: You are not allowed to create
'Point of Sale Category' (pos.category) records.

This commit solves the above issue by allowing the creation of demo
data on POS for users, which has User rights.

sentry-4245391993

closes odoo/odoo#127263

X-original-commit: a8f5343f5b83f6eb069f9d1e542fc1e14fbedfcb
Signed-off-by: David Monnom (moda) <moda@odoo.com>

addons/point_of_sale/models/pos_session.py

@@ -2108,7 +2108,7 @@ class PosSession(models.Model):
     def load_product_frontend(self):
         allowed = not self._pos_has_valid_product()
         if allowed:
-            self._load_onboarding_data()
+            self.sudo()._load_onboarding_data()
 
         return {
             'models_data': self.get_onboarding_data(),