Support multiple subnets

[jrouly]

Is your feature request related to a problem? Please describe.

FSx and FileCache only support single AZs. However, my workers on EKS span many AZs. I would like for the CSI driver to be able to create a PVC backed by FSx in any of the available subnets for the cluster.

Describe the solution you'd like in detail

• Provision one SC backed by the fsx-csi-driver with multiple subnets or a subnet selector specified.
• When a pod is created using the SC, any of the available subnets can be selected to provision the FSx volume and the pod will be scheduled in the selected subnet.

Describe alternatives you've considered

The current strategy means that every workload scheduled to use the fsx CSI driver will be scheduled in a single AZ. This will cause pretty severe imbalance on my EKS cluster.