How to add extra option to WP core gallery block?

I want to add the extra option to the “Link to” attribute of “core/gallery” WP block. As default, It has three options,
enter image description here

  1. Attachment page
  2. Medial file
  3. None

I want to add extra option to the existing three and make them like

  1. Attachment page
  2. Medial file
  3. None
  4. Custom

Any help would be appreciated.