Add modal component to V3

[dpikt]

A redo of #426 that doesn't rely on the unmerged style branch. Since this is a new component, requiring a style change to use it is not technically breaking 🙂

Author Checklist

• [x] Add unit test(s)
• [x] Update version in package.json
• [x] Update documentation (if necessary)
• [x] Add story to storybook (if necessary)
• [x] Assign dev reviewer