TOC sections cannot be toggled with keyboard

[arlina-espinoza]

Describe the bug
The sections on the left table of contents cannot be toggled (open/close) via keyboard, only with a mouse.

Expected behavior
The sections should be expanded/collapsed when they have keyboard focus and expand/collapse with the space bar.

How to reproduce

1. Go to example page on Chrome: https://redocly.github.io/redoc/
2. Tab to get to a section like "Upcoming Events".
3. Press space to try to open/close - nothing happens.

Recommendations

• Ensure there is a button role either by making the control a <button> element or adding role="button" to the element
• Make the control focusable either by making it a <button> element or adding tabindex="0"
• Ensure the button can be activated with the ENTER and SPACE keys
• Add an accessible name to the button by adding an aria-label to the button or <div role="button">. Additionally, ensure the value updates when the double arrow icon updates to an "X" icon that closes the disclosure.
• Add the aria-expanded attribute to the button. When content is expanded, aria-expanded="true", when it is collapsed, aria-expanded="false"