Clarify remote_cluster_client role (#70186)

This commit addresses two aspects of the description in the docs of
configuring a local node to be a remote cluster client. First, the
documentation was referring to the legacy setting for configuring a
remote cluster client. Secondly, we clarify that additional features,
not only cross-cluster search, have requirements around the usage of the
remote_cluster_client role.

Co-authored-by: Przemysław Witek <przemyslaw.witek@elastic.co>
Co-authored-by: James Rodewig <40268737+jrodewig@users.noreply.github.com>

docs/reference/ccr/getting-started.asciidoc

@@ -83,6 +83,12 @@ indices on the local cluster. <<stack-management-ccr-local,Configure local clust
 * An index on the remote cluster that contains the data you want to replicate.
 This tutorial uses the sample eCommerce orders data set.
 {kibana-ref}/get-started.html#gs-get-data-into-kibana[Load sample data].
+* In the local cluster, all nodes with the `master` <<node-roles,node role>> must
+  also have the <<remote-node,`remote_cluster_client`>> role. The local cluster
+  must also have at least one node with both a data role and the
+  <<remote-node,`remote_cluster_client`>> role. Individual tasks for coordinating
+  replication scale based on the number of data nodes with the
+  `remote_cluster_client` role in the local cluster.
 
 [[ccr-getting-started-remote-cluster]]
 ==== Connect to a remote cluster

docs/reference/modules/remote-clusters.asciidoc

@@ -258,13 +258,16 @@ separately.
   The time to wait for remote connections to be established when the node
   starts. The default is `30s`.
 
-`node.remote_cluster_client`::
+`remote_cluster_client` <<node-roles,role>>::
 
   By default, any node in the cluster can act as a cross-cluster client and
-  connect to remote clusters. The `node.remote_cluster_client` setting can be
-  set to `false` (defaults to `true`) to prevent certain nodes from connecting
-  to remote clusters. Remote cluster requests must be sent to a node that is
-  allowed to act as a cross-cluster client.
+  connect to remote clusters. To prevent a node from connecting to remote
+  clusters, specify the <<node-roles,node.roles>> setting in `elasticsearch.yml`
+  and exclude `remote_cluster_client` from the listed roles. Search requests
+  targeting remote clusters must be sent to a node that is allowed to act as a
+  cross-cluster client. Other features such as {ml} <<general-ml-settings,data
+  feeds>>, <<general-transform-settings,transforms>>, and
+  <<ccr-getting-started,{ccr}>> require the `remote_cluster_client` role.
 
 `cluster.remote.<cluster_alias>.skip_unavailable`::