Kubernetes StatefulSet itself doesn't allow volumes to be added to StatefulSets after their initial creation.

Trying to add a volume, results in this error:
Forbidden: updates to statefulset spec for fields other than 'replicas', 'template', 'updateStrategy', 'persistentVolumeClaimRetentionPolicy' and 'minReadySeconds' are forbidden

The same limitation is encountered via operator.

• create StatefulSet by setting:

spec:
  statefulSet: {}

• try to add a volume to it

spec.
  statefulSet: 
    storage:
      size: 100Mi
      mountPath: /logs

Tasks:

• understand the reasons behind StatefulSet not supporting
• if it's not an anti-pattern to add volume afterwards, support adding it via operator. StatefulSet probably have to be deleted and recreated (meaning there will be some downtime)