[DOCS] Adds documentation on telemetry settings (elastic#50739)

* [DOCS] Adds documentation on telemetry settings

* [DOCS] Adds not that both settings can't be false at the same time

docs/setup/settings.asciidoc

@@ -319,6 +319,18 @@ supported protocols with versions. Valid protocols: `TLSv1`, `TLSv1.1`, `TLSv1.2
 setting this to `true` enables unauthenticated users to access the Kibana server
 status API and status page.
 
+`telemetry.allowChangingOptInStatus`:: *Default: true*. If `true`, 
+users are able to change the telemetry setting at a later time in 
+<<advanced-options, Advanced Settings>>.  If `false`, 
+{kib} looks at the value of `telemetry.optIn` to determine whether to send 
+telemetry data or not. `telemetry.allowChangingOptInStatus` and `telemetry.optIn`
+cannot be `false` at the same time.
+
+`telemetry.optIn`:: *Default: true* If `true`, telemetry data is sent to Elastic. 
+ If `false`, collection of telemetry data is disabled.  
+ To enable telemetry and prevent users from disabling it,
+ set `telemetry.allowChangingOptInStatus` to `false` and `telemetry.optIn` to `true`.
+
 `vega.enableExternalUrls:`:: *Default: false* Set this value to true to allow Vega to use any URL to access external data sources and images. If false, Vega can only get data from Elasticsearch.
 
 `xpack.license_management.enabled`:: *Default: true* Set this value to false to