Update ECK documentation for rotating credentials. (#3488)

## Question

- Do we want to also document how to rotate the Kibana encryption keys?

Related: elastic/cloud-on-k8s#8839

---------

Signed-off-by: Michael Montgomery <[email protected]>
Co-authored-by: shainaraskas <[email protected]>

Author: naemono

deploy-manage/users-roles/cluster-or-deployment-auth/managed-credentials-eck.md

@@ -68,12 +68,30 @@ If you are using the `elastic` user credentials in your own applications, they w
 
 To regenerate all auto-generated credentials in a namespace, run the following command:
 
+::::{warning}
+The following command regenerates auto-generated credentials of **all** {{stack}} applications in the namespace.
+::::
+
+::::{applies-switch}
+
+:::{applies-item} { "eck": "ga 3.2" }
+In ECK versions 3.2 and beyond:
+
 ```sh
 kubectl delete secret -l eck.k8s.elastic.co/credentials=true
 ```
 
-::::{warning}
-This command regenerates auto-generated credentials of **all** {{stack}} applications in the namespace.
+:::
+
+:::{applies-item} { "eck": "ga 3.1" }
+In ECK versions prior to 3.2:
+
+```sh
+kubectl delete secret -l eck.k8s.elastic.co/credentials=true,common.k8s.elastic.co/type!=kibana
+```
+
+:::
+
 ::::
 
 ### Control the length of auto-generated passwords