feat: Modal Component

[callinmullaney]

Summary

• Adds a boilerplate modal component to compound.

This PR fixes/implements the following bugs/features

• Implements basic principles of collapsible sections (https://inclusive-components.design/collapsible-sections/) to create a modal component that is accessible and keyboard-friendly.

Explain the motivation for making this change. What existing problem does the pull request solve?

• Modals are a very common method of displaying content. It has been a prioritized component defined within the Emulsify UI-Kit initiative.

Documentation Update (required)

• None

How to review this PR

• [x] checkout branch and run npm install then npm run storybook
• [x] Go to Molecules/Modal and confirm you can see multiple modal options. The functionality for each should be the same. The differences center around the markup that triggers the modal which can be any type of markup. It does not have to be triggered from a button/link only.
• [x] Use your keyboard to focus and trigger the modal. Verify the link within the modal is focus-able once the modal is active and pressing the esc closes the modal
• [x] Review the twig and styles and verify they are a good starting point for future projects and arent too opinionated.

[callinmullaney]

@mndonx Thank you for the thorough review! I addressed your inline comments and added variable/block documentation for the twig file. I also made adjustments to the default colors we're using to help address the contrast warnings you mentioned. This will affect all components so hopefully should eliminate this accessibility error for others once merged.

One accessability error you will come across when re-testing is Ensures tabindex attribute values are not greater than 0 - This is intentional as it plays into the keyboard-trap JS and allows the modal to draw focus above everything else on a page.

Lastly, I fixed the icon display issue. Looks like the webpack script needed to explicitly point to the ./images/icons folder and not just ./images

[callinmullaney]

@joetower @ryanhagerty Adding you to this PR to help move things along if you have time. Can you confirm I addressed Amanda's feedback from above and let me know if this is ready for an accessibility review?