manual-ca-rotation: adjust note for "--client-ca-file"

- Instead of telling the users to remove the flag, tell them
that they can point to a copy of the new CA for --client-ca-file
--cluster-signing-cert-file that is not in a bundle with the old CA.
- Don't reference the kubeadm issue. If sig-auth has a tracking
issue for --client-ca-file / --cmanual-ca-rotation: adjust note for "--client-ca-file"

- Instead of telling the users to remove the --client-ca-file flag,
tell them that they can point to a copy of the new CA.
Mention the same for --cluster-signing-cert-file.
- Don't reference the kubeadm issue. If sig-auth has a tracking
issue for --client-ca-file / --cluster-signing-cert-file and bundles
we can add that at some point.

Author: neolit123

content/en/docs/tasks/tls/manual-rotation-of-ca-certificates.md

@@ -38,9 +38,11 @@ Configurations with a single API server will experience unavailability while the
    Any service account created after this point will get secrets that include both old and new CAs.
 
    {{< note >}}
-   Remove the flag `--client-ca-file` from the *Kubernetes controller manager* configuration.
-   You can also replace the existing client CA file or change this configuration item to reference a new, updated CA.
-   [Issue 1350](https://github.com/kubernetes/kubeadm/issues/1350) tracks an issue with *Kubernetes controller manager* being unable to accept a CA bundle.
+   The files specified by the *Kubernetes controller manager* flags `--client-ca-file` and `--cluster-signing-cert-file`
+   cannot be CA bundles. If these flags and `--root-ca-file` point to the same `ca.crt` file which is now a
+   bundle (includes both old and new CA) you will face an error. To workaround this problem you can copy the new CA to a separate
+   file and make the flags `--client-ca-file` and `--cluster-signing-cert-file` point to the copy. Once `ca.crt` is no longer
+   a bundle you can restore the problem flags to point to `ca.crt` and delete the copy.
    {{< /note >}}
 
 1. Update all service account tokens to include both old and new CA certificates.