Add shouldAutoFocus prop to Overlay, SideSheet, and Dialog components

[brandongregoryscott]

Resolves #1404

Overview

This PR introduces a prop to Overlay, SideSheet and Dialog that allows a consumer to disable the default autofocus behavior that lives in Overlay.js. As noted in that task, there are certain cases where the behavior can be incorrect or undesirable but there's no obvious way to opt out of it. This PR addresses that - retaining the current behavior, but opening up a way to disable it if needed.

Screenshots (if applicable)

Behavior can be demoed in the respective Storybook areas:

https://deploy-preview-1535--evergreen-storybook.netlify.app/?path=/story/overlay--autofocus-disabled

https://deploy-preview-1535--evergreen-storybook.netlify.app/?path=/story/side-sheet--autofocus-disabled

(Scroll to bottom and click button 'Show Dialog with autofocus disabled') https://deploy-preview-1535--evergreen-storybook.netlify.app/?path=/story/dialog--dialog

Documentation

• [x] Updated Typescript types and/or component PropTypes
• [x] Added / modified component docs
• [x] Added / modified Storybook stories

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