update migration link and add 7.0 release notes

[netlify[bot]]

✅ Deploy Preview for storybook-frontpage ready!

Name	Link
🔨 Latest commit	0ad06fa92bb5f191b7f9395af61241a538a21630
🔍 Latest deploy log	https://app.netlify.com/sites/storybook-frontpage/deploys/6426ef976f7cda00087e186b
😎 Deploy Preview	https://deploy-preview-509--storybook-frontpage.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site settings.