Update socket-dir

[Akrog]

Originally socket-dir for the pods had to be on /var/lib/kubelet/plugins/<driver-name>/csi.sock, as described in the documentation, but this is no longer the case. Now sidecars accept an argument with the address to use to connect to the CSI plugin, so we can use an emptyDir instead of a fixed path.

This will be required to be able to do rolling upgrades, as we'll have multiple instances of the plugin running simultaneous while we update/upgrade.

We should update the operator to use emptyDir when the sidecar containers allow it, to support rolling upgrades.