If a visitor tries to send a file too large, they will get a message after a while that an error occurred. The message isn't specific enough. With this commit: - when a visitor sends a form, a spinner will appear indicating that the file is being uploaded. - if the upload fails because the file is too large, the user will be notified. task-2234699 closes odoo/odoo#70301 Signed-off-by: Jérémy Kersten (jke) <jke@openerp.com> Co-authored-by: Romain Derie <rde@odoo.com> Co-authored-by: Arthur Detroux <ard@odoo.com>