Update vm.max_map_count value in "Configure a RHEL host" doc (#4376)

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This is part of work in
elastic/docs-content-internal#592. We are
upgrading `vm.max_map_count` value in "Configure a RHEL host" doc to
reflect the correct value.

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Author: kunisen

deploy-manage/deploy/cloud-enterprise/configure-host-rhel.md

@@ -317,7 +317,7 @@ Verify that required traffic is allowed. Check the [Networking prerequisites](ec
     ```sh
     cat <<EOF | sudo tee -a /etc/sysctl.conf
     # Required by Elasticsearch
-    vm.max_map_count=262144
+    vm.max_map_count=1048576
     # enable forwarding so the Docker networking works as expected
     net.ipv4.ip_forward=1
     # Decrease the maximum number of TCP retransmissions to 5 as recommended for Elasticsearch TCP retransmission timeout.