[ADD] client_notification: Add the new client_notification module

    - The 'client_notification' module was added.
    - A new client_notification model was introduced, including fields and methods to manage notifications in a generic and modular way.
    - A Scheduled Action (ir.cron) was added to call the _send_notifications method for each client_notification record. Depending on the implementation, this could either send a generic request or invoke a specific method.
    - List, kanban, and form views to manage client_notifications were added.
    - The 'confisa_notification' module was added. This module introduces a new client_notification record called "Confisa Client Notification".
    - This module also adds the necessary methods to interact with the Confisa API. It sends notifications when a Sale Order is canceled or when a task related to a Sale Order is completed.
    - Adding unittests