Added server.defaultRoute (#9075)

* Added server.defaultRoute

* Update settings.asciidoc

docs/setup/settings.asciidoc

@@ -14,6 +14,7 @@ you'll need to update your `kibana.yml` file. You can also enable SSL and set a
  to Kibana. This setting cannot end in a slash (`/`).
 `server.maxPayloadBytes:`:: *Default: 1048576* The maximum payload size in bytes for incoming server requests.
 `server.name:`:: *Default: "your-hostname"* A human-readable display name that identifies this Kibana instance.
+`server.defaultRoute:`:: *Default: "/app/kibana"* This setting specifies the default route when opening Kibana. You can use this setting to modify the landing page when opening Kibana.
 `elasticsearch.url:`:: *Default: "http://localhost:9200"* The URL of the Elasticsearch instance to use for all your
 queries.
 `elasticsearch.preserveHost:`:: *Default: true* When this setting’s value is true Kibana uses the hostname specified in