feat: Add custom link modal

[suzubara]

Description

This PR uses a branch of ReactUSWDS that adds the Modal component (trussworks/react-uswds#1622) and sets up a modal root element so we can render modals in the portal app. It builds off #249 to add a modal to that flow where a user can enter a label for a custom link.

Fixes #246

Review Notes

• Verify you can add a link to an existing collection and be prompted to enter a label for the link.
• The link label is a required field and you cannot save a link without entering something.
• Since the link is only added in the local cache, refreshing the page will reset any changes you've made.

addLink.mp4

[suzubara]

All Modal components should be wrapped in this <ModalPortal> component, in order to be rendered into the modal-root element.

[github-actions]

🎉 View the deployed prototype - https://246-add-modals--ussf-portal-client.netlify.app

[jbecker01]

@suzubara There's a bug where:

• I add a new custom link, give it a title and save it
• I delete the new custom link
• When I click on the Add Site button again, I'm immediately presented with the link name modal instead of being able to add the URL first.
• If I add a name and then click save, a new link is created with the URL that I just deleted.

Would you like a new issue for this?

[suzubara]

@suzubara There's a bug where:

• I add a new custom link, give it a title and save it
• I delete the new custom link
• When I click on the Add Site button again, I'm immediately presented with the link name modal instead of being able to add the URL first.
• If I add a name and then click save, a new link is created with the URL that I just deleted.

Would you like a new issue for this?

@jbecker01 nice find!! No thanks, I will resolve it in this PR

[abbyoung]

Another bug that seems related to John's:

• Successfully add bookmark
• Click Add Link to add another
• Get the 'We don't recognize that link' modal immediately without entering a link
• If I enter a label, it adds with the previous url

[suzubara]

@jbecker01 @abbyoung both of the above issues should be resolved now!

[suzubara]

Use this when writing Jest tests for modal components (or components that render modals)

[github-actions]

🎉 View the deployed prototype - https://246-add-modals--ussf-portal-client.netlify.app

[abbyoung]

Jest: "global" coverage threshold for functions (95%) not met: 94.9% Thanks, I hate it! 😭

[jbecker01]

Looks good to me!

[github-actions]

🎉 View the deployed prototype - https://246-add-modals--ussf-portal-client.netlify.app

[abbyoung]

looks great! 🎉