[MERGE][ADD] website{_profile,_slides,_forum,*} : new profile page yayy

Purpose of this merge is to provide a completely new and improved user profile
page linked to gamification, slides and forum. Those frontend applications
now heavily rely on website profile and add their own custom content like
channel or forum participation or challenges results. This merge is linked
to the currently under development eLearning feature [1][2].

This merge contains notably

 * review website profile page centralized in a new module : website_profile;
 * move everything that was linked to the profile from website_forum in
   website_profile;
 * properly add forum informations in website_forum through inheritance;
 * add channel / course informations in website_slides through inheritance;

A new bridge module is added that is website_slide_forum. It makes a link
between those two applications. Publishers can create a forum linked to a
course allowing participants to communicate and ask questions related to a
course.

Profile page is contextualized. When coming from a channel informations about
this channel is displayed. Linked forum information is added. When coming from
a specific forum only information related to this forum is displayed.
Otherwise a profile page with aggregated information is displayed.

Some other improvements are done: ranks, karma, badges from gamification are
included in forum and eLearning, 'new badge notifications' mechanism is removed
as email are send, and various other improvements. See sub commits for more
details.

Merge linked to task ID 1922159.

[1] see task ID 1902304 (main eLearning task) PR #29876;
[2] see task ID 1936153 (new homepage for slides) PR #30770;

closes odoo/odoo#30988