Notifications Improvements

[ziming]

1. Documentation to tell us an easy way to generate a link to a nova resource detail page.

Currently I do something like this which is not ideal

Notification::send(Admin::first(), \Laravel\Nova\Notifications\NovaNotification::make()
            ->message('New Post!')
            ->action('View', '/resources/posts/' . 42) // any built in way to pass in the Resource class and id?
            ->icon('book-open')
            ->type('success')
        );

2. Allow us to specify for a longer notification bar width in config

3. Shows the date & time of each notification