In the section "Enabling automatic sidecar injection" we say that a user must add an annotation 'sidecar.istio.io/inject: "true"'.
Since this annotation was depracated in upstream Istio in favor of a label with the same name, we should say that we support annotations and labels, but users should prefer the label, because the annotation is deprecated. It does not require any release note, because we didn't change anything in maistra/istio.

Related upstream doc: https://istio.io/latest/docs/setup/additional-setup/sidecar-injection/