docs: add warning about athena usage with exporter (#32121)

docs/pages/reference/audit.mdx

@@ -46,7 +46,7 @@ used, events are written to the filesystem in JSON format. The `dir` backend rot
 the event file approximately once every 24 hours, but never deletes captured events.
 
 For High Availability configurations, users can refer to our
-[Athena](./backends.mdx#athena), [DynamoDB](./backends.mdx#dynamodb) or
+[Athena](./backends.mdx#athena-preview), [DynamoDB](./backends.mdx#dynamodb) or
 [Firestore](./backends.mdx#firestore) chapters for information on how to
 configure the SSH events and recorded sessions to be stored on network storage.
 When these backends are in use, audit events will eventually expire and be

docs/pages/reference/backends.mdx

@@ -946,7 +946,26 @@ Config option priority is applied in the following order:
   are not supported in certain regions or environments or are only supported in GovCloud.
 </Admonition>
 
-## Athena
+## Athena (Preview)
+
+The Athena audit log back-end is available starting from Teleport v14.0, and is
+currently in preview.
+
+<Notice type="danger">
+
+If you are using the
+[Teleport-event-exporter](../management/export-audit-events/fluentd.mdx)
+or any other mechanism for polling of [SearchEvents
+API](https://pkg.go.dev/github.com/gravitational/teleport/api/client#Client.SearchEvents),
+you should not use the Athena audit back-end, as the preview release of this
+back-end is especially resource intensive when polling the Teleport Auth
+Service for audit events.
+
+A new version of the Teleport event handler is under development to address this
+issue.
+
+</Notice>
+
 
 If you are running Teleport on AWS, you can use an
 [Athena](https://aws.amazon.com/athena/)-based audit log system that manages