Add notes for smtp server removal

Refs getsentry/sentry#58361

src/docs/self-hosted/releases.mdx

@@ -64,3 +64,9 @@ We provide nightly builds from the [master branch of the self-hosted repository
 - [Symbolicator](https://github.com/getsentry/symbolicator)
 
 These builds are usually stable, but you may occasionally hit a broken version as these versions are not guaranteed to be deployed to [sentry.io](http://sentry.io/) first. There is also no guarantee that you will be able to do a clean upgrade to later versions without losing any data. **Use the nightly builds at your own risk.**
+
+## Breaking Changes
+
+- The `23.11.0` release will remove the ``sentry run smtp`` worker process. This
+ worker was not part of the standard self-hosted configuration, but could be
+ used in custom deployments.