We only document updating the `Istio` resource, but users will also need to update the `IstioCNI` resource once all control planes have been updated to complete the OSSM upgrade procedure.

According to the Istio Ambient upgrade documentation, "The CNI at version 1.x is compatible with the control plane at version 1.x+1 and 1.x. This means the control plane must be upgraded before Istio CNI, as long as their version difference is within one minor version." Our upgrade instructions should include this guidance.

This is same guidance should likely apply to OSSM (ambient mode or sidecar). Thus, once users have upgraded all control planes, they should upgrade IstioCNI.
 
This does not appear to be covered in sail-operator community doc either, so should be added there as well.