add support for other options with PVC

[edevosc2c]

• Allow the ability to specify an empty storageClassName which disable automatic provisioning of the PVC. See https://github.com/helm/helm/issues/2600
• Allow the ability to configure accessModes. For example for PV hosted on NFS. Example

I did try to use helm helper for that now that there is a lot of redundancy but failed to because $webapp and $webapp_storage are dynamic. May try in another PR.