docs: note CLI incompatibilities (#14049) (#14060)

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

docs/operator-manual/upgrading/2.6-2.7.md

@@ -90,3 +90,19 @@ If your environment uses Kustomize JSON patches to modify the Redis server name,
 to the 2.7 manifests. If it does, you can remove the patch and instead set the Redis server name via the `redis.server` 
 field in the argocd-cmd-params-cm ConfigMap. That value will be passed to the necessary components via `valueFrom` 
 environment variables.
+
+## `argocd applicationset` CLI incompatibilities for ApplicationSets with list generators
+
+If you are running Argo CD v2.7.0-2.7.2 server-side, then CLI versions outside that range will incorrectly handle list
+generators. That is because the gRPC interface for those versions used the `elements` field number for the new
+`elementsYaml` field.
+
+If you are running the Argo CD CLI versions v2.7.0-2.7.2 with a server-side version of v2.7.3 or later, then the CLI
+will send the contents of the `elements` field to the server, which will interpret it as the `elementsYaml` field. This
+will cause the ApplicationSet to fail at runtime with an error similar to this:
+
+```
+error unmarshling decoded ElementsYaml error converting YAML to JSON: yaml: control characters are not allowed
+```
+
+Be sure to use CLI version v2.7.3 or later with server-side version v2.7.3 or later.