Use emptyDir if no PVC should be created

Fix #267 (closed), depends on !192 (merged).

helm/preconfigs/oci.yaml

 operator:
   resultsVolume:
-    storageClassName: "oci-bv"
-    size: 50Gi # minimal size in OCI
\ No newline at end of file
+    persistent:
+      enabled: true
+      storageClassName: "oci-bv"
+      size: 50Gi # minimal size in OCI