Fix <ColumnsButton> cannot be used with keyboard

[djhi]

Problem

• Although it's possible to open the <ColumnsButton> menu with space, it's impossible to reach its items using the keyboard.
• It also produce invalid HTML when adding the filter (not rendered inside a li element)

Solution

• Make it possible to reach its items using the keyboard.
• Produce valid HTML

Note: Drag and dropping the items to reorder columns has not been implemented yet.

How To Test

• Story
• Click in the background around the list t ofocus the story iframe
• Press Tab until the <ColumnsButton> is active
• Press Space to open its menu
• Press Tab to loop through its items, toggling them with Space
• Press Escape to close the menu

Additional Checks

• The PR targets master for a bugfix or a documentation fix, or next for a feature