Accessibility: CheckboxButtonGroup should have a fieldset/legend structure.

[oasisrising]

Duplicates

• I have searched the existing issues

Latest version

• I have tested the latest version

Current behavior 😯

Grouped controls should be part of a fieldset:
https://www.w3.org/WAI/tutorials/forms/grouping/#checkboxes

Expected behavior 🤔

Example with fieldset and legend components set on the MUI components:
https://mui.com/material-ui/react-checkbox/#formgroup

Steps to reproduce 🕹

Steps: