[FIX] web: allow any levels in navbar menus

In 14.0 the menu items in the navbar sections menu could have any level.
Since the webclient refactoring landed in 15.0 0573acae this feature has
been unintentionnally limited to two levels.
More sub menus would simply not be displayed.

**Before this commit**
- Have a menu item with the following path:
  `App/Menu/Group/Sub-group/Item`
- The `Sub-group` is displayed as an item. It is clickable but nothing happens.
- The `Item` is not displayed.

**After this commit**
Works properly as it should. See screenshots on the PR description.

closes odoo/odoo#121039

Signed-off-by: Mathieu Duckerts-Antoine <dam@odoo.com>
Co-authored-by: Mathieu Duckerts-Antoine <dam@odoo.com>