Update sample app dependencies

[devisscher]

Updating the template to use App Bridge React V4.

This PR does:

• Update the readme with troubleshooting steps if your app is looping or not rendering in admin
• Removes unnecessary imports in sample-apps/discounts/app/entry.server.jsx to use built in Response object
• Adds App Bridge React V4 CDN script to head of the app in: sample-apps/discounts/app/root.jsx and load apiKey from env vars.
• Remove old usage of App Bridge React V3 in sample-apps/discounts/app/routes/app.jsx
• Update the create and edit routes to use new App Bridge React patterns for navigation
• Update page layouts to use ui-title-bar
• Update dependencies in package.json

This PR can be merged after a new version of discount-app-components is released: https://github.com/Shopify/discount-app-components/pull/203

[devisscher]

This is part of fixing: https://github.com/Shopify/core-issues/issues/68945