Clarify master-to-cluster-manager name change in index.md (#8784)

In #7660 there was an effort to find-and-replace `master` with `cluster manager`. In this one particular case it was unwarranted however, as the sentence is explaining how master nodes are now called cluster manager nodes.

I also simplified the sentence, as the "nomenclature" part is unnecessary.

Signed-off-by: Benjamin Wolak <bwolak@crunchbase.com>

Author: bwolak

_tuning-your-cluster/index.md

@@ -20,7 +20,7 @@ To create and deploy an OpenSearch cluster according to your requirements, it’
 
 There are many ways to design a cluster. The following illustration shows a basic architecture that includes a four-node cluster that has one dedicated cluster manager node, one dedicated coordinating node, and two data nodes that are cluster manager eligible and also used for ingesting data.
 
-  The nomenclature for the cluster manager node is now referred to as the cluster manager node.
+  The master node is now referred to as the cluster manager node.
    {: .note }
 
 ![multi-node cluster architecture diagram]({{site.url}}{{site.baseurl}}/images/cluster.png)