OSDOCS-6777 updated ossm prereqs for ROSA

Author: xJustin

service_mesh/v2x/installing-ossm.adoc

@@ -15,7 +15,12 @@ This basic installation is configured based on the default OpenShift settings an
 
 .Prerequisites
 * Read the xref:../../service_mesh/v2x/preparing-ossm-installation.adoc#preparing-ossm-installation[Preparing to install {SMProductName}] process.
+ifdef::openshift-rosa[]
+* An account with the `cluster-admin` role.
+endif::openshift-rosa[]
+ifndef::openshift-rosa[]
 * An account with the `cluster-admin` role. If you use {product-dedicated}, you must have an account with the `dedicated-admin` role.
+endif::openshift-rosa[]
 
 The following steps show how to install a basic instance of {SMProductName} on {product-title}.