FormGroup: need to be able to set items div wrapper/group classname

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Describe the bug The FromGroup items are wrapped with a div but there is no option/prop to set the class in this div. I propose a prop called "itemGroupClassName"

To Reproduce Use the FormGroup in a React app and observe the div wrapping the list of radios/checkboxes and attempt to set a class name for this wrapping container

Expected behavior To be able to set a class name on the div wrapping the list of items/radios/checkboxes

Screenshots If applicable, add screenshots to help explain your problem.

Desktop (please complete the following information): N/A Smartphone (please complete the following information): N/A

Additional context N/A