Add docs for 'delete unenrolled agents' (#1383) (#1399)

* Add docs for 'delete unenrolled agents'

* Update docs/en/ingest-management/fleet/fleet-settings.asciidoc

Co-authored-by: Julia Bardi <[email protected]>

---------

Co-authored-by: Julia Bardi <[email protected]>
(cherry picked from commit 2a9b034)

Co-authored-by: David Kilfoyle <[email protected]>

Author: mergify[bot]

docs/en/ingest-management/fleet/fleet-settings.asciidoc

@@ -132,3 +132,16 @@ in the agent policy.
 
 You can specify a proxy server to be used in {fleet-server}, {agent} outputs, or for any agent binary download sources. 
 For full details about proxy configuration refer to <<fleet-agent-proxy-support,Using a proxy server with {agent} and {fleet}>>.
+
+[discrete]
+[[delete-unenrolled-agents-setting]]
+== Delete unenrolled agents
+
+After an {agent} has been unenrolled in {fleet}, a number of documents about the agent are retained just in case the agent needs to be recovered at some point. You can choose to have all data related to an unenrolled agent deleted automatically.
+
+Note that this option can also be enabled by adding the `xpack.fleet.enableDeleteUnenrolledAgents: true` setting to the {kibana-ref}/[{kib} settings file].
+
+To enable automatic deletion of unenrolled agents:
+
+. Go to **{fleet} -> Settings**.
+. Under **Advanced Settings**, enable the **Delete unenrolled agents** option.