[Suggestion] Add a Fieldset element

[teenwolfblitzer]

Description

Groups of related form elements (checkboxes and radio buttons in particular) stand to benefit from the addition of a Sage fieldset (and legend).

• Using a fieldset will clearly define the relationship between controls to screen readers
• Developers will gain the ability to enable and disable entire sets of controls at once
• Testing can be simplified by allowing grouped form controls to be scoped under a single test_id

Discussion points/considerations

• Styling fieldset styling: remove border and padding as defaults?
• Intended for functional use only, not as a styled "container"
• legend should be required but provide an option to visually hide

Additional Information

• MDN
• https://accessibility.blog.gov.uk/2016/07/22/using-the-fieldset-and-legend-elements/