[5.x] Offer "Stay signed in" in session renewal modal

[redburn]

The full login page offers the option to stay signed in for 2 weeks, but the "session ended" modal does not. I think this would be helpful, otherwise users can get stuck in a loop of having to sign in again and again when they forgot to tick the box initially.

Added this local hook temporarily as a workaround:

        Event::on(
            View::class,
            View::EVENT_BEFORE_RENDER_TEMPLATE,
            function (TemplateEvent $event) {
                if (
                    $event->template !== '_special/login-modal.twig' ||
                    !empty($event->variables['forElevatedSession'])
                ) {
                    return;
                }

                $event->variables['showRememberMeCheckbox'] = true;
            }
        );