This patch removes the `with_service` helper from the code base.
Instead, we can pass a block with actions directly to the `.call` method
of a service.
This simplifies how to use services:
- use `.call` without a block to run the service and get its result
object.
- use `.call` with a block of actions to run the service and execute
arbitrary code depending on the service outcome.
It also means a service is now “self-contained” and can be used anywhere
without having to include a helper or whatever.
* DEV: Add a dedicated Admin::StaffController base controller
The current parent(Admin:AdminController) for all admin-related controllers
uses a filter that allows only staff(admin, moderator) users.
This refactor makes Admin::AdminController filter for only admins as the name suggests and
introduces a base controller dedicated for staff-related endpoints.
* DEV: Set staff-only controllers parent to Admin::StaffController
Refactor staff-only controllers to inherit newly introduced
Admin::StaffController abstract controller. This conveys the
purpose of the parent controller better unlike the previously used parent
controller.
