containerd: add migration guide

[dvdksn]

trafficstars

Description

This PR adds a migration guide to help users enable the containerd image store while also migrating image/container data from the classic store.

[netlify[bot]]

✅ Deploy Preview for docsdocker ready!

Name	Link
🔨 Latest commit	c86c3837b7cac3f142423d3f613730dd7398c974
🔍 Latest deploy log	https://app.netlify.com/sites/docsdocker/deploys/66631898c25a1a0008518e95
😎 Deploy Preview	https://deploy-preview-20180--docsdocker.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 configuration.

[docker-robot[bot]]

Thanks for the pull request. We'd like to make our product docs better, but haven’t been able to review all the suggestions. As our docs have also diverged, we do not have the bandwidth to review and rebase old pull requests.

If the updates are still relevant, review our contribution guidelines and rebase your pull request against the latest version of the docs, then mark it as fresh with a /remove-lifecycle stale comment. If not, this pull request will be closed in 30 days. This helps our maintainers focus on the active pull requests.

Prevent pull requests from auto-closing with a /lifecycle frozen comment.

/lifecycle stale