Enhance ECE post-installation steps (#3910)

Added steps to ECE post install doc:
* configuring ECE system deployments 
* setting up traffic filters for enhanced security.
* move nodes off from an allocator
* configure deployment templates

Steps taken from
https://www.elastic.co/guide/en/cloud-enterprise/3.8/ece-getting-started-post-installation.html

Author: eedugon

deploy-manage/deploy/cloud-enterprise/post-installation-steps.md

@@ -18,6 +18,12 @@ To start creating {{es}} deployments directly, refer to [](./working-with-deploy
 
 * Add your own [load balancer](./ece-load-balancers.md). Load balancers are user supplied and we do not currently provide configuration steps for you.
 
+* [Add more capacity](/deploy-manage/maintenance/ece/scale-out-installation.md) to your ECE installation, [resize your deployment](./resize-deployment.md), [upgrade to a newer {{es}} version](/deploy-manage/upgrade/deployment-or-cluster/upgrade-on-ece.md), and [add some plugins](./add-plugins.md).
+
+* [Configure ECE system deployments](./system-deployments-configuration.md) to ensure a highly available and resilient setup.
+
+* [Configure ECE for deployment templates](./configure-deployment-templates.md) to indicate what kind of hardware you have available for {{stack}} deployments.
+
 * In production systems, add your own [Cloud UI and Proxy certificates](../../security/secure-your-elastic-cloud-enterprise-installation/manage-security-certificates.md) to enable secure connections over HTTPS. The proxy certificate must be a wildcard certificate signed for the needed DNS records of your domain.
 
   ::::{note}
@@ -32,19 +38,21 @@ To start creating {{es}} deployments directly, refer to [](./working-with-deploy
   For example, if your proxy certificate is signed for `*.elastic-cloud-enterprise.example.com` and you have a wildcard DNS register pointing `*.elastic-cloud-enterprise.example.com` to your load balancer, you should configure `elastic-cloud-enterprise.example.com` as the **deployment domain name** in Platform → Settings. Refer to [](./change-endpoint-urls.md) for more details.
   ::::
 
-* If you received a license from Elastic, [manage the licenses](../../license/manage-your-license-in-ece.md) for your {{ece}} installation.
+* [Add a snapshot repository](../../tools/snapshot-and-restore/cloud-enterprise.md) to enable regular backups of your {{es}} clusters.
 
 * [Add more platform users](../../users-roles/cloud-enterprise-orchestrator/manage-users-roles.md) with role-based access control.
 
-* [Add a snapshot repository](../../tools/snapshot-and-restore/cloud-enterprise.md) to enable regular backups of your {{es}} clusters.
-
 * Consider enabling encryption-at-rest (EAR) on your hosts.
 
   :::{{note}}
   Encryption-at-rest is not implemented out of the box in {{ece}}. [Learn more](/deploy-manage/security/secure-your-elastic-cloud-enterprise-installation.md#ece_encryption).
   :::
 
-* Learn about common maintenance activities—such as adding capacity, applying OS patches, and addressing host failures--at [](../../maintenance/ece.md).
+* Set up [traffic filters](/deploy-manage/security/network-security.md) to restrict traffic to your deployment to only trusted IP addresses or VPCs.
+
+* Learn how to work around host maintenance or a host failure by [moving nodes off of an allocator](/deploy-manage/maintenance/ece/move-nodes-instances-from-allocators.md). For an overview of common ECE maintenance activities, refer to [ECE maintenance](../../maintenance/ece.md).
+
+* If you received a license from Elastic, [manage the licenses](../../license/manage-your-license-in-ece.md) for your {{ece}} installation.
 
 ::::{warning}
 During installation, the system generates secrets that are placed into the `/mnt/data/elastic/bootstrap-state/bootstrap-secrets.json` secrets file, unless you passed in a different path with the --host-storage-path parameter. Keep the information in the `bootstrap-secrets.json` file secure by removing it from its default location and placing it into a secure storage location.