Fix control for withCheckAll to be boolean

[BoppLi]

for the purpose of the storybook examples, it's enough to offer a boolean control for "withCheckAll".

Problem:

That does not solve the issue: the URL's "true" setting for withCheckAll is still ignored.

Original Description:

https://storybook.onyx.schwarz/?path=/story/form-select--grouped-options&args=multiple:!true;open:!true;withSearch:!true;withCheckAll:!true
-> the link was created with

but when you open the link/ reload you only get

=> "withCheckAll" also has a combined type