Update shared-monitor-config.asciidoc monitoring.cluster_uuid missing (…

…elastic#31867) (elastic#31934) (elastic#31944)

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

Co-authored-by: Jennie Soria <predogma@users.noreply.github.com>
(cherry picked from commit 146cf2e)

libbeat/docs/monitoring/shared-monitor-config.asciidoc

@@ -32,6 +32,10 @@ The default value is `false`.
 The {es} instances that you want to ship your {beatname_uc} metrics to. This
 configuration option contains the following fields:
 
+==== `monitoring.cluster_uuid`
+
+The `monitoring.cluster_uuid` config identifies the {es} cluster under which the monitoring data will appear in the Stack Monitoring UI. 
+
 ===== `api_key`
 
 The detail of the API key to be used to send monitoring information to {es}.