add not recommended banner

docs/en/observability/apm/apm-performance-diagnostic.asciidoc

@@ -40,7 +40,7 @@ See {metricbeat-ref}/exported-fields-beat.html[{metricbeat} documentation] for t
 
 One likely cause of excessive indexing pressure or rejected requests is undersized {es}. To mitigate this, follow the guidance in {ref}/rejected-requests.html[Rejected requests].
 
-If scaling {es} resources up is not an option, you can adjust the `flush_bytes`, `flush_interval`, `max_retries` and `timeout` settings described in <<apm-elasticsearch-output,Configure the Elasticsearch output>> to reduce APM Server indexing pressure. However, consider that increasing number of buffered documents and/or reducing retries may lead to a higher rate of dropped APM events. Down below a custom configuration example is listed where the number of default buffered documents is roughly doubled while {es} indexing retries are decreased simultaneously. This configuration provides a generic example and might not be applicable to your situation. Try adjusting the settings further to see what works for you.
+(Not recommended) If scaling {es} resources up is not an option, you can adjust the `flush_bytes`, `flush_interval`, `max_retries` and `timeout` settings described in <<apm-elasticsearch-output,Configure the Elasticsearch output>> to reduce APM Server indexing pressure. However, consider that increasing number of buffered documents and/or reducing retries may lead to a higher rate of dropped APM events. Down below a custom configuration example is listed where the number of default buffered documents is roughly doubled while {es} indexing retries are decreased simultaneously. This configuration provides a generic example and might not be applicable to your situation. Try adjusting the settings further to see what works for you.
 [source,yaml]
 ----
 output.elasticsearch: