[REF] website_slides: make eLearning an application with its own menu structure

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

Update manifest and make website_slides an application separated from
website embedded menus.

Implement new menu structure

  * Courses
    * Courses
      List view: Course Name, # Views, # Attendees, # Ratings, Revenues,
      Reviews
    * Contents

  * Reporting
    * Courses: list view on slide.channel model, ordered by # views.
        * add a graph view (group by content)
    * Contents: graph view on slide.slide model
        Area Graph: X month
        Y measure: # Views (others measures: Attendees, ...)
        Group by: course (color)
    * Reviews: see kanban of latest reviews;
    * Quiz: list view on slide.question model.
        List view: Add # Quizz Trials, # Quizz Passed, Avg Attempts

  * Configuration
    * Settings
      * Allow Forum on Courses (installs website_slides_forum)
      * Allow Certifications (installs website_slides_survey)
      * Allow Selling Courses (installs website_sale_slides)
    * Course Tags
      * See channel.tags.group with label Course Tags, form view allow to
        configure group tags
      * https://drive.google.com/a/odoo.com/file/d/1G0g2UnG5cZG55EXQ5icbgwe7T2eSZskT/view?usp=drivesdk
      * On click: open :https://drive.google.com/a/odoo.com/file/d/1I_PW3aZAbrslXadiYqmVF-_6dGXx8knd/view?usp=drivesdk


    * Content Tags

This structure will gain new items in sub-modules, notably bridge with
form and website_sale. Those will be implemented in next commits.

LINKS

Task 1978729
PR #35061

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