[FEATURE] EKS Pod Identity support

### Describe the feature

Currently, Apache Gravitino only supports IAM Roles for Service Accounts (IRSA) for AWS authentication within EKS clusters.

I would like to propose adding support for EKS Pod Identity. This modern authentication method simplifies credential management by allowing IAM roles to be mapped directly to Kubernetes Service Accounts without the need for OIDC provider configuration.

https://docs.aws.amazon.com/en_us/eks/latest/userguide/pod-identities.html#pod-id-benefits

### Motivation

_No response_

### Describe the solution

_No response_

### Additional context

_No response_

The issue names no implementation files or tests. Start by locating Gravitino's existing IRSA authentication path and read the linked AWS EKS Pod Identity documentation; done means supporting Pod Identity alongside IRSA with appropriate tests and documentation.

Written by the indexing model from the issue text.