Add the option to use checkboxes.

Hi @kevinfunk,

I've attempted to apply your patch to the selected version "8.x-1.x-dev" of the module. However, I encountered challenges in applying it successfully. While I did manage to get the select and checkbox selection field, the transformation of the schema from a select list to checkboxes did not occur as expected.

I kindly request your assistance in creating a Merge Request (MR) for this patch.

Thank you

Patch #2 works for using using Drupal 10.2.5