'Update the user objectives (`target_sales_done`, target_sales_won`
and `target_sales_invoiced` fields).
:param target_name : part of the fields name to update
:param target_value : value of the field to update'

@api.model
def modify_target_sales_dashboard(self, target_name, target_value):

    if (target_name in ['won', 'done', 'invoiced']):
        self.env.user.write({('target_sales_' + target_name): target_value})
    else:
        raise UserError(_('This    target    does    not    exist.'))
