Backport: docs: add migration guide for v6 (#10639)

This is an automated backport of #10636 to the release-v5.0 branch. FYI
@nicoalbanese

Co-authored-by: Nico Albanese <[email protected]>
Co-authored-by: vercel[bot] <35613825+vercel[bot]@users.noreply.github.com>

Author: 3 people

content/docs/08-migration-guides/27-migration-guide-6-0.mdx

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+---
+title: Migrate AI SDK 5.0 to 6.0 Beta
+description: Learn how to upgrade AI SDK 5.0 to 6.0 Beta.
+---
+
+# Migrate AI SDK 5.0 to 6.0 Beta
+
+<Note type="warning">
+  AI SDK 6 is currently in beta and introduces new capabilities like agents and
+  tool approval. This guide will help you migrate from AI SDK 5.0 to 6.0 Beta.
+  Note that you may want to wait until the stable release for production
+  projects. See the [AI SDK 6 Beta announcement](/docs/announcing-ai-sdk-6-beta)
+  for more details on what's new.
+</Note>
+
+## Recommended Migration Process
+
+1. Backup your project. If you use a versioning control system, make sure all previous versions are committed.
+1. Upgrade to AI SDK 6.0 Beta.
+1. Follow the breaking changes guide below.
+1. Verify your project is working as expected.
+1. Commit your changes.
+
+## AI SDK 6.0 Beta Package Versions
+
+You need to update the following packages to the beta versions in your `package.json` file(s):
+
+- `ai` package: `6.0.0-beta` (or use the `@beta` dist-tag)
+- `@ai-sdk/provider` package: `3.0.0-beta` (or use the `@beta` dist-tag)
+- `@ai-sdk/provider-utils` package: `4.0.0-beta` (or use the `@beta` dist-tag)
+- `@ai-sdk/*` packages: `3.0.0-beta` (or use the `@beta` dist-tag for other `@ai-sdk` packages)
+
+An example upgrade command would be:
+
+```
+pnpm install ai@beta @ai-sdk/react@beta @ai-sdk/openai@beta
+```
+
+## Codemods
+
+The AI SDK **will** provide Codemod transformations to help upgrade your codebase when a
+feature is deprecated, removed, or otherwise changed.
+
+Codemods are transformations that run on your codebase automatically. They
+allow you to easily apply many changes without having to manually go through
+every file.
+
+<Note>
+  Codemods are intended as a tool to help you with the upgrade process. They may
+  not cover all of the changes you need to make. You may need to make additional
+  changes manually.
+</Note>
+
+## Codemod Table
+
+| Codemod Name | Description |
+| ------------ | ----------- |
+| TBD          | TBD         |