Add deprecation banner to docs

[mrbbot]

This PR adds a banner to the top of the Miniflare 2 docs (https://miniflare.dev), warning users that Miniflare 2 is no longer supported aside from security updates.

This required patching the cloudflare-docs-engine. The old cloudflare-docs-engine has quite a complicated setup process, so rather than doing this with patch-package, I've just pushed my patches to a new branch on that repo (cloudflare/cloudflare-docs-engine@master...bcoll/miniflare-2-banner) and updated the commit hash here.

[changeset-bot]

⚠️ No Changeset found

Latest commit: 5d40644

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR