docs: add astream v2 migration guide links (#21845)

- docs: v0.2 version sidebar
- x
- x

docs/docs/versions/v0_2/index.mdx

@@ -11,6 +11,7 @@ LangChain v0.2 was released in May 2024. This release includes a number of [brea
 :::note Reference
 
 - [Breaking Changes & Deprecations](/docs/versions/v0_2/deprecations)
+- [Migrating to Astream Events v2](/docs/versions/v0_2/migrating_astream_events)
 
 :::
 
@@ -23,6 +24,7 @@ This documentation will help you upgrade your code to LangChain `0.2.x.`. To pre
 3. Install a recent version of `langchain-cli` , and use the tool to replace old imports used by your code with the new imports. (See instructions below.)
 4. Manually resolve any remaining deprecation warnings.
 5. Re-run unit tests.
+6. If you are using `astream_events`, please review how to [migrate to astream events v2](/docs/versions/v0_2/migrating_astream_events).
 
 ## Upgrade to new imports