FQ: Basic environment variable support

[KyleSanderson]

When this is fixed (if it ever worked?) it would be very useful to align to the well established variables present in in the retail upstream NFS provisioner using pathPattern. I see there's some basic ones now, but it doesn't help to actually place data correctly.

As an example: ${.PVC.namespace}/${.PVC.name}${.PVC.annotations.nfs.io/storage-path}

docs: https://github.com/kubernetes-sigs/nfs-subdir-external-provisioner