Improve csi-snapshotter ClusterRole

[andyzhangx]

Is your feature request related to a problem?/Why is this needed

Describe the solution you'd like in detail

With v2.0.0 of kubernetes-csi/external-snapshotter, it is split into two component - the csi-snapshotter sidecar and the snapshot controller (ref kubernetes-csi/external-snapshotter#182). As the VolumeSnapshot watch is moved to the new snapshot controller, the csi-snapshotter sidecar ClusterRole no longer needs rules for volumesnapshots.
This PR adapts the csi-snapshotter sidecar RBAC according to https://github.com/kubernetes-csi/external-snapshotter/blob/v2.1.1/deploy/kubernetes/csi-snapshotter/rbac-csi-snapshotter.yaml.

refer to kubernetes-sigs/aws-ebs-csi-driver#491

Describe alternatives you've considered

Additional context