Add 6.4.0 release highlights for the distributed area (#32795)

docs/reference/release-notes/highlights-6.4.0.asciidoc

@@ -32,3 +32,12 @@ See also <<release-notes-6.4.0,{es} 6.4.0 release notes>>.
 * Cross Cluster Search will no longer use dedicated master nodes as gateway nodes - Previously the gateway node on a remote cluster used by Cross Cluster search was selected based only on the node's version and node attributes set in the `search.remote.node.attr` setting. This meant that unless carefully configured any node in the cluster could potentially be used as a gateway node for a cross cluster search. This may cause problems when running with dedicated master nodes as it is undesirable for master eligible nodes to be used for any search activity. Starting from 6.4.0 cross cluster search will no longer consider dedicated master eligible nodes as potential gateway nodes providing a better out of the box default for running cross cluster searches.
 * Format option for doc_value fields - `doc_value` fields in the Search API can now specify a `format` field to control the format of the value in the response. For more information, see <<search-request-docvalue-fields, doc_value fields>>.
 * Support second level of field collapse -  This extends the field collapsing feature to allow the top item for two fields to be retrieved. For example retrieving top scored tweets by country, and for each country, top scored tweets for each user. This can be an alternative to using multiple levels of terms aggregations along with top hits. For more information, see <<search-request-collapse,Field Collapsing>>.
+
+[float]
+=== Snapshot and Restore
+
+6.4.0 has seen a great amount of small improvements to the Snapshot and Restore. No less than https://github.com/elastic/elasticsearch/pulls?q=is%3Aclosed+is%3Apr+label%3A%3ADistributed%2FSnapshot%2FRestore+label%3Av6.4.0[53] S&R related changes went into this release. The 
+changes ranges include https://github.com/elastic/elasticsearch/pulls?q=is%3Aclosed+is%3Apr+label%3A%3ADistributed%2FSnapshot%2FRestore+label%3Av6.4.0+label%3A%3Etest[improving testing infra structure], https://github.com/elastic/elasticsearch/pull/30435[tightening] https://github.com/elastic/elasticsearch/pull/30438[up] https://github.com/elastic/elasticsearch/pull/30439[calls] https://github.com/elastic/elasticsearch/pull/30439[to] Cloud providers API and https://github.com/elastic/elasticsearch/pull/30168[upgrading underlying 3rd party libraries]. 
+
+Specifically we want to highlight the https://github.com/elastic/elasticsearch/pull/30414[added support for AWS session tokens] to both 
+the EC2 discovery plugin and the S3 repository plugins. This allows Elasticsearch to use AWS devices protected by multi factor authentication.