"scylla" chart ignores provided storage class

[vponomaryov]

Describe the bug
File located at "helm/scylla/templates/cluster.yaml" has following line for setting k8s storage class:
storageClassName: {{ .storage.className }}

Doc located at "docs/source/scylla_cluster_crd.md" says following:

  datacenter:
    name: us-east-1
    racks:
      - name: us-east-1a
        members: 3
        storage:
          capacity: 500G
          storageClassName: local-raid-disks

But "helm/scylla/values.schema.json" one has following:

  "storage": {
      "type": "object",
      "properties": {
          "capacity": {
              "type": "string"
          }
      }
  }

And when storage class is provided to the chart it ignores it and default storage class is used.

To Reproduce
Steps to reproduce the behavior:

1. Deploy scylla-operator
2. Create scylla chart providing there non-default storage class
3. See that scylla PVCs get created using default storage class

Expected behavior
PVCs use provided non-default storage class

Config Files
If relevant, upload your configuration files here using GitHub, there is no need to upload them to any 3rd party services

Logs
Please, provide kubectl get events, kubectl logs -n scylla pod-name and other relevant information.

Environment:

• Platform: GKE
• Kubernetes version: v1.17.15-gke.800
• Scylla version: 4.2.0
• Scylla-operator version: v1.1.0-rc.4-0-g8f2cec5

Additional context
Add any other context about the problem here.