[REF] website_sale_slides: improve integration into eLeaning application

PURPOSE

eLearning should have its own application in manager. Indeed this is becoming
a big application and having it embedded inside Website application is not
enough anymore. It should also hold updated and easy-to-use menus,
navigation, actions and views in backend.

SPECIFICATIONS

Improve course form view: add a revenue stat button displaying the total
of sale order linked to the course's product.

Add in slide.channel kanban card
  * Add "Sales       150.00$" below "Watch Time" if type "on payment". Same
    info than the smart/stat button on the course itself. Click on the amount
    sends to Reporting Revenues (same than on the stat btn)

Add menu entry inside Reporting
    * Revenues: graph view on sale.report model showing revenues of eLearning
      courses.
        Area chart, X: month Y: €, Color: course

LINKS

Task 1978729
PR #35061

Co-Authored-By: Thibault Delavallée <tde@odoo.com>
Co-Authored-By: Jérémy Hennecart <jeh@odoo.com>