Add switch flag to make checkboxes switches

[jankapunkt]

Bootstrap 4.2 introduced switches for checkboxes and it would be great to make checkboxes switches. Config could like so:

{
  agree: {
    type: Boolean,
    autoform: {
      type: 'checkbox',
      switch: true
    }
  }
}

This would however require the checkbox to be a custom form control but I think this is a good idea for the long term.