Before this commit, it was only possible to add attachments on documents from the backend or by sending them by email. It is now possible to add them also from the portal chatter, including for portal/public users who have a valid access_token. Part of task-37264 closes odoo/odoo#34526 Signed-off-by: Olivier Dony (odo) <odo@openerp.com> Co-authored-by: Pratima Gupta <pgu@odoo.com> Co-authored-by: Sébastien Theys <seb@odoo.com>