Changes to spec.meshconfig are not picked up immediately

Currently, when making a change to spec.meshconfig that influences e.g. sidecar injection, those changes are not immediately applied, because istiod does not watch the ConfigMap for changes. When users edit meshconfig in the SMCP, they still have to manually do

kubectl rollout restart deployment istiod

to apply their new meshconfig.

We should look into automating this- we're offering an operator after all, so we can react to changes in the ConfigMap. The simplest way would be to add an annotation to the istiod pod that holds the SHA256 of the relevant ConfigMaps, as described in the helm docs: Automatically Roll Deployments.