Allow override all available settings

Looks good

Looks good + this patch also fix an issue with placeholder from v2 which prevented slim select from using Drupal translation. It was using the default "Select Value" settings from slim_select library:

Change from:

placeholder = placeholderText

To

placeholderText = placeholderText

Thank you for your work, it is merged

Automatically closed - issue fixed for 2 weeks with no activity.