Adding enterprise search comments and links to ECK 2.16 docs (#1062)

ECK 3.0 still supports Enterprise Search for deployments running 8.x
versions of Elastic Stack (and maybe even 7.17, although that's
irrelevant for the PR).

We had removed almost all references to Enterprise Search during the
migration and that will look odd considering that some users might still
run ECK-managed deployments with Enterprise Search.

This PR adds mentions to Enterprise Search in 3 different docs,
including links to the 2.16 version of ECK documentation:

- [Stack helm chart
utilization](https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/1062/deploy-manage/deploy/cloud-on-k8s/managing-deployments-using-helm-chart#k8s-install-enterprise-search-elasticsearch-kibana-helm)
- [Orchestrating other elastic stack
applications](https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/1062/deploy-manage/deploy/cloud-on-k8s/orchestrate-other-elastic-applications)
- [Network policies
examples](https://docs-v3-preview.elastic.dev/elastic/docs-content/pull/1062/deploy-manage/security/k8s-network-policies#k8s-network-policies-enterprise-search-isolation)

Another approach for this would be to bring back all content related to
Enterprise Search from older docs, but maybe it's better this way.

@shainaraskas , @bmorelli25 : I'd need to know if the links I'm using
for the older documents are correct in terms of destination.

And extra question for doc stakeholders:
- What should we do with URL mappings of those components? For example
https://www.elastic.co/guide/en/cloud-on-k8s/current/k8s-enterprise-search.html
and all childs have been removed in the new docs system. Should we
create redirects or something to point them to the 2.16 version of the
docs? or should they all be mapped to the new version of the docs that
tells users that Enterprise Search is not supported in 9.x and link to
the 2.16 docs?

---------

Co-authored-by: shainaraskas <[email protected]>

Author: eedugon

deploy-manage/deploy/cloud-on-k8s/managing-deployments-using-helm-chart.md

@@ -80,7 +80,11 @@ helm install eck-stack-with-apm-server elastic/eck-stack \
     --values https://raw.githubusercontent.com/elastic/cloud-on-k8s/2.16/deploy/eck-stack/examples/apm-server/basic.yaml -n elastic-stack
 ```
 
-## Install individual components of the {{stack}} [k8s-eck-stack-individual-components] 
+## Enterprise Search server along with {{es}} and {{kib}} [k8s-install-enterprise-search-elasticsearch-kibana-helm]
+
+Enterprise Search is not available in {{stack}} versions 9.0 and later. For an example deployment of {{es}} version 8.x, {{kib}} 8.x, and an 8.x Enterprise Search server using the Helm chart, refer to the [previous ECK documentation](https://www.elastic.co/guide/en/cloud-on-k8s/2.16/k8s-stack-helm-chart.html).
+
+## Install individual components of the {{stack}} [k8s-eck-stack-individual-components]
 
 You can install individual components in one of two ways using the provided Helm Charts.
 

deploy-manage/deploy/cloud-on-k8s/orchestrate-other-elastic-applications.md

@@ -14,6 +14,10 @@ The following guides provide specific instructions for deploying and configuring
 * [Beats](beats.md)
 * [{{ls}}](logstash.md)
 
+::::{note}
+Enterprise Search is not available in {{stack}} versions 9.0 and later. To deploy or manage Enterprise Search in earlier versions, refer to the [previous ECK documentation](https://www.elastic.co/guide/en/cloud-on-k8s/2.16/k8s-enterprise-search.html).
+::::
+
 When orchestrating any of these applications, also consider the following topics:
 
 * [{{stack}} Helm Chart](managing-deployments-using-helm-chart.md)

deploy-manage/security/k8s-network-policies.md

@@ -433,3 +433,6 @@ spec:
       common.k8s.elastic.co/type: logstash
 ```
 
+## Isolating Enterprise Search [k8s-network-policies-enterprise-search-isolation]
+
+Enterprise Search is not available in {{stack}} versions 9.0 and later. For an example of Enterprise Search isolation using network policies in previous {{stack}} versions, refer to the [previous ECK documentation](https://www.elastic.co/guide/en/cloud-on-k8s/2.16/k8s_prerequisites.html#k8s-network-policies-enterprise-search-isolation).