Pod Impersonation for IAM

[adammw]

Is your feature request related to a problem? Please describe.
Currently, IAM role permissions must be assigned to the CSI driver itself rather than the pods that mount the volumes, leaving permissions of preventing which pods can mount these volumes as an exercise to the cluster administrator.

Describe the solution you'd like in detail
AWS EFS CSI Driver can impersonate the pod service account identity and exchange that identity for an IAM role that is used for mounting, instead of the CSI driver's native IAM identity.

Describe alternatives you've considered
n/a

Additional context
#885 seems to describe a similar feature, but was closed by automation