Add key prop to Select component option

[yurm04]

WHY are these changes introduced?

Fixes #11111 issue where you have two identical option values that trigger a React key warning.

WHAT is this pull request doing?

Adds an optional key prop to Select component options. If the key prop is undefined the key will default to the option value (which is the current behavior)

How to 🎩

🖥 Local development instructions
🗒 General tophatting guidelines
📄 Changelog guidelines

Copy-paste this code in playground/Playground.tsx:

import React from 'react';
import {Page} from '../src';

export function Playground() {
  return (
    <Page title="Playground">
      {/* Add the code you want to test in here */}
    </Page>
  );
}

🎩 checklist

• Tested on mobile
• Tested on multiple browsers
• Tested for accessibility
• Updated the component's README.md with documentation changes
• Tophatted documentation changes in the style guide

[kyledurand]

👍