Using manually created PVs/PVCs as volumes in container of deployment

[samox73]

I have mounted an EFS from AWS into my current grafana deployment to keep grafana as stateless as possible with minimal cost. However, I do not see how I would go about overwriting the storageVolume and storageVolumeMount to use my manually defined values. I could open a PR which makes configuring the volumes possible, if there is no other way to achieve this.