[DOCS] Add Beats config example for ingest pipelines (#78633)

* [DOCS] Add Beats config example for ingest pipelines

The Elasticsearch ingest pipeline docs cover ingest pipelines for Fleet and
Elastic Agent. However, the docs don't cover Beats. This adds those docs.

Relates to https://github.com/elastic/beats/pull/28239.

* Update docs/reference/ingest.asciidoc

Co-authored-by: DeDe Morton <dede.morton@elastic.co>

Co-authored-by: DeDe Morton <dede.morton@elastic.co>

docs/reference/ingest.asciidoc

@@ -271,6 +271,21 @@ Use the <<index-final-pipeline,`index.final_pipeline`>> index setting to set a
 final pipeline. {es} applies this pipeline after the request or default
 pipeline, even if neither is specified.
 
+[discrete]
+[[pipelines-for-beats]]
+=== Pipelines for {beats}
+
+To add an ingest pipeline to an Elastic Beat, specify the `pipeline`
+parameter under `output.elasticsearch` in `<BEAT_NAME>.yml`. For example,
+for {filebeat}, you'd specify `pipeline` in `filebeat.yml`.
+
+[source,yaml]
+----
+output.elasticsearch:
+  hosts: ["localhost:9200"]
+  pipeline: my-pipeline
+----
+
 [discrete]
 [[pipelines-for-fleet-elastic-agent]]
 === Pipelines for {fleet} and {agent}