[NET-4122] Doc guidance for federation with externalServers (#18207)

Doc guidance for federation with externalServers

Add guidance for proper configuration when joining to a secondary
cluster using WAN fed with external servers also enabled.

Also clarify federation requirements and fix formatting for an
unrelated value.

Update both the Helm chart reference (synced from `consul-k8s`, see
hashicorp/consul-k8s#2583) and the docs on using `externalServers`.

website/content/docs/k8s/deployment-configurations/servers-outside-kubernetes.mdx

@@ -114,6 +114,10 @@ to create policies, tokens, and an auth method. If you are [enabling Consul serv
 so that the Consul servers can validate a Kubernetes service account token when using the [Kubernetes auth method](/consul/docs/security/acl/auth-methods/kubernetes)
 with `consul login`.
 
+-> **Note:** If `externalServers.k8sAuthMethodHost` is set and you are also using WAN federation 
+(`global.federation.enabled` is set to `true`), ensure that `global.federation.k8sAuthMethodHost` is set to the same 
+value as `externalServers.k8sAuthMethodHost`.
+
 <CodeBlockConfig filename="values.yaml">
 
 ```yaml

website/content/docs/k8s/helm.mdx

@@ -484,8 +484,9 @@ Use these links to navigate to a particular top-level stanza.
     - `enabled` ((#v-global-federation-enabled)) (`boolean: false`) - If enabled, this datacenter will be federation-capable. Only federation
       via mesh gateways is supported.
       Mesh gateways and servers will be configured to allow federation.
-      Requires `global.tls.enabled`, `meshGateway.enabled` and `connectInject.enabled`
-      to be true. Requires Consul 1.8+.
+      Requires `global.tls.enabled`, `connectInject.enabled`, and one of 
+      `meshGateway.enabled` or `externalServers.enabled` to be true.
+      Requires Consul 1.8+.
 
     - `createFederationSecret` ((#v-global-federation-createfederationsecret)) (`boolean: false`) - If true, the chart will create a Kubernetes secret that can be imported
       into secondary datacenters so they can federate with this datacenter. The
@@ -497,8 +498,8 @@ Use these links to navigate to a particular top-level stanza.
 
     - `primaryDatacenter` ((#v-global-federation-primarydatacenter)) (`string: null`) - The name of the primary datacenter.
 
-    - `primaryGateways` ((#v-global-federation-primarygateways)) (`array<string>: []`) - A list of addresses of the primary mesh gateways in the form `<ip>:<port>`.
-      (e.g. ["1.1.1.1:443", "2.3.4.5:443"]
+    - `primaryGateways` ((#v-global-federation-primarygateways)) (`array<string>: []`) - A list of addresses of the primary mesh gateways in the form `<ip>:<port>`
+      (e.g. `["1.1.1.1:443", "2.3.4.5:443"]`).
 
     - `k8sAuthMethodHost` ((#v-global-federation-k8sauthmethodhost)) (`string: null`) - If you are setting `global.federation.enabled` to true and are in a secondary datacenter,
       set `k8sAuthMethodHost` to the address of the Kubernetes API server of the secondary datacenter.
@@ -507,6 +508,9 @@ Use these links to navigate to a particular top-level stanza.
       from the one used by the Consul Service Mesh.
       Please refer to the [Kubernetes Auth Method documentation](/consul/docs/security/acl/auth-methods/kubernetes).
 
+      If `externalServers.enabled` is set to true, `global.federation.k8sAuthMethodHost` and 
+      `externalServers.k8sAuthMethodHost` should be set to the same value.
+
       You can retrieve this value from your `kubeconfig` by running:
 
       ```shell-session
@@ -1120,6 +1124,9 @@ Use these links to navigate to a particular top-level stanza.
     This address must be reachable from the Consul servers.
     Please refer to the [Kubernetes Auth Method documentation](/consul/docs/security/acl/auth-methods/kubernetes).
 
+    If `global.federation.enabled` is set to true, `global.federation.k8sAuthMethodHost` and 
+    `externalServers.k8sAuthMethodHost` should be set to the same value.
+
     You could retrieve this value from your `kubeconfig` by running:
 
     ```shell-session