Support pod identity for storage authentication

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

Use pod identity is better from a security point of view compared to regular secrets (SAS or blob access keys). Easier to manage, distribute etc.

**Describe the solution you'd like in detail**

Add support for authentication to storage with managed identity in addition to SAS/account token.

**Describe alternatives you've considered**

**Additional context**

The issue does not name files or tests. Start by locating the existing SAS and account-token authentication paths in the kubernetes-volume-drivers repository, then trace how storage credentials reach the volume driver. Done means storage authentication also works through Kubernetes pod identity or Azure managed identity without requiring SAS or account keys.

Written by the indexing model from the issue text.