[DOCS] Adds monitoring breaking change (#31369)

Author: lcawl

docs/reference/migration/migrate_6_3.asciidoc

@@ -94,3 +94,11 @@ place) you can start Elasticsearch with the JVM option
 `-Des.thread_pool.write.use_bulk_as_display_name=true` to have Elasticsearch
 continue to display the name of this thread pool as `bulk`. Elasticsearch will
 stop observing this system property in 7.0.0.
+
+==== Enabling monitoring 
+
+By default when you install {xpack}, monitoring is enabled but data collection
+is disabled. To enable data collection, use the new
+`xpack.monitoring.collection.enabled` setting. You can update this setting by
+using the <<cluster-update-settings,Cluster Update Settings API>>. For more
+information, see <<monitoring-settings>>.