Add Mutating webhook to modify the monitoring and logging stack

[afritzler]

Summary

Use a similar approach used in the local Gardener provider to mutate the monitoring/logging components to modify the deployment of those: https://github.com/gardener/gardener/tree/master/pkg/provider-local/webhook/prometheus

That way we can scale down e.g. Prometheus to a single replica deployment and reduce the disk size used via its PVC.