[MERGE] website_forum, *: revamp design

* portal, website, website_event, website_sale, website_mail,
  website_slides_forum, web_editor, website_profile

See sub-commits for details.

task-2024197

closes odoo/odoo#35749

Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>
Co-authored-by: sri-odoo <sri@odoo.com>
Co-authored-by: Jérémy Kersten <jke@odoo.com>
Co-authored-by: qsm-odoo <qsm@odoo.com>
Co-authored-by: fja-odoo <fja@odoo.com>