[EKS][eks-pod-identity]: EKS Pod Identity STS packedPolicySize is too large when chaining roles

### Summary

I want to use EKS Pod Identities as credentials source for my application, which uses Role Chaining to assume other roles.
My application also relies on set of required Session Tags that should be passed to when assuming the role, however AssumeRole call is failing with:

```json
"errorCode": "PackedPolicyTooLargeException",
"errorMessage": "Packed size of session tags consumes 112% of allotted space.",
```

I performed set of tests to record `packedPolicySize` value in CloudFront events:

Test | packedPolicySize | Comment
----|--------------------|----------
Assuming role **without EKS Pod Identities** with required custom Session Tags | 37 | This is a baseline of policy size required by my application.
Assuming role **with EKS Pod Identity** with required custom Session Tags | 112 | PackedPolicyTooLargeException
Assuming role **with EKS Pod Identity** without any session tags | 74 | ❗️ EKS Pod Identity session by itself consumes 74% of the limit ❗️

Based on the above, we can see that assuming role using EKS Pod Identity leaves only 26% of PackedPolicyLimit, which is not enough for any type of custom ABAC policies.

Documentation regarding Transitive Tag keys[^1] can be confusing and was recently updated to change the wording regarding the limits:
[^1]: https://docs.aws.amazon.com/STS/latest/APIReference/API_AssumeRole.html

```diff
TransitiveTagKeys.member.N
A list of keys for session tags that you want to set as transitive. If you set a tag key as transitive, the corresponding key and value passes to subsequent sessions in a role chain. For more information, see [Chaining Roles with Session Tags](https://docs.aws.amazon.com/IAM/latest/UserGuide/id_session-tags.html#id_session-tags_role-chaining) in the IAM User Guide.

- This parameter is optional. When you set session tags as transitive, the session policy and session tags packed binary limit is not affected.
+ This parameter is optional. The transitive status of a session tag does not impact its packed binary size.
```

------

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The report provides no repository files, tests, or implementation entry point. Start by reviewing the linked AWS STS AssumeRole and session-tag documentation, then investigate how EKS Pod Identity credentials are generated and chained; done means role chaining supports the required session tags without PackedPolicyTooLargeException.

Written by the indexing model from the issue text.