[IMP] web: formview auto close dialog

Sometimes when using a form view in a modal (e.i.: in a gantt view), we might
want to have some button in the footer. We expect clicking on buttons to close
the dialog but nothing happens, since the webclient does not know that this is
a modal.
To do so, we provide the `close='1'` attribute on the button, in form view.
This will trigger the event closing the modal.

This is done with the benediction of aab-odoo

Task-2024216

closes odoo/odoo#36493

Signed-off-by: Jérome Maes (jem) <jem@openerp.com>