docs: Consul on Kubernetes specific upgrade info (#18230)

* Compatibility page - dataplanes mention

* Upgrading higher-level dataplane mention

* `exec=` string callout

* More visible for upgrade page

* Apply suggestions from code review

Co-authored-by: Tu Nguyen <im2nguyen@users.noreply.github.com>

---------

Co-authored-by: Tu Nguyen <im2nguyen@users.noreply.github.com>
Co-authored-by: John Murret <john.murret@hashicorp.com>

website/content/docs/k8s/compatibility.mdx

@@ -11,14 +11,20 @@ For every release of Consul on Kubernetes, a Helm chart, `consul-k8s-control-pla
 
 ## Supported Consul and Kubernetes versions
 
-Consul Kubernetes versions all of its components (`consul-k8s` CLI, `consul-k8s-control-plane`, and Helm chart) with a single semantic version. When installing or upgrading to a specific versions, ensure that you are using the correct Consul version with the compatible `consul-k8s` helm chart and/or CLI.
+Consul Kubernetes versions all of its components (`consul-k8s` CLI, `consul-k8s-control-plane`, and Helm chart) with a single semantic version. When installing or upgrading to a specific versions, ensure that you are using the correct Consul version with the compatible Helm chart or `consul-k8s` CLI.
 
-| Consul Version | Compatible consul-k8s Versions   | Compatible Kubernetes Versions | 
+| Consul version | Compatible `consul-k8s` versions | Compatible Kubernetes versions |
 | -------------- | -------------------------------- | -------------------------------|
 | 1.16.x         | 1.2.x                            | 1.24.x - 1.27.x                |
 | 1.15.x         | 1.1.x                            | 1.23.x - 1.26.x                |
 | 1.14.x         | 1.0.x                            | 1.22.x - 1.25.x                |
 
+### Version-specific upgrade requirements
+
+As of Consul v1.14.0, Kubernetes deployments use [Consul Dataplane](/consul/docs/connect/dataplane) instead of client agents. If you upgrade Consul from a version that uses client agents to a version that uses dataplanes, you must follow specific steps to update your Helm chart and remove client agents from the existing deployment. Refer to [Upgrading to Consul Dataplane](/consul/docs/k8s/upgrade#upgrading-to-consul-dataplane) for more information.
+
+The v1.0.0 release of the Consul on Kubernetes Helm chart also introduced a change to the [`externalServers[].hosts` parameter](/consul/docs/k8s/helm#v-externalservers-hosts). Previously, you were able to enter a provider lookup as a string in this field. Now, you must include `exec=` at the start of a string containing a provider lookup. Otherwise, the string is treated as a DNS name. Refer to the [`go-netaddrs`](https://github.com/hashicorp/go-netaddrs) library and command line tool for more information.
+
 ## Supported Envoy versions
 
 Supported versions of Envoy and `consul-dataplane` (for Consul K8s 1.0 and above) for Consul versions are also found in [Envoy - Supported Versions](/consul/docs/connect/proxies/envoy#supported-versions). Starting with `consul-k8s` 1.0, `consul-dataplane` will include a bundled version of Envoy. The recommended best practice is to use the default version of Envoy or `consul-dataplane` that is provided in the Helm `values.yaml` file, as that is the version that has been tested with the default Consul and Consul Kubernetes binaries for a given Helm chart.

website/content/docs/k8s/upgrade/index.mdx

@@ -5,14 +5,23 @@ description: >-
   Consul on Kubernetes relies on packages and binaries that have individual upgrade requirements. Learn how to update Helm configurations, Helm versions, Consul versions, and Consul agents, as well as how to determine what will change and its impact on your service mesh.
 ---
 
-# Upgrading Consul on Kubernetes Components
+# Upgrading Consul on Kubernetes components
+
+This topic describes considerations and strategies for upgrading Consul deployments running on Kubernetes clusters. In addition to upgrading the version of Consul, you may need to update your Helm chart or the release version of the Helm chart.
+
+## Version-specific upgrade requirements
+
+As of Consul v1.14.0, Kubernetes deployments use [Consul Dataplane](/consul/docs/connect/dataplane) instead of client agents. If you upgrade Consul from a version that uses client agents to a version that uses dataplanes, you must follow specific steps to update your Helm chart and remove client agents from the existing deployment. Refer to [Upgrading to Consul Dataplane](/consul/docs/k8s/upgrade#upgrading-to-consul-dataplane) for more information.
+
+The v1.0.0 release of the Consul on Kubernetes Helm chart also introduced a change to the [`externalServers[].hosts` parameter](/consul/docs/k8s/helm#v-externalservers-hosts). Previously, you were able to enter a provider lookup as a string in this field. Now, you must include `exec=` at the start of a string containing a provider lookup. Otherwise, the string is treated as a DNS name. Refer to the [`go-netaddrs`](https://github.com/hashicorp/go-netaddrs) library and command line tool for more information.
 
 ## Upgrade types
 
 We recommend updating Consul on Kubernetes when:
+
   - You change your Helm configuration
   - A new Helm chart is released
-  - You want to upgrade your Consul version.
+  - You want to upgrade your Consul version
 
 ### Helm configuration changes