fix: Invoke aws_iam_session_context data source only when required

[krlydm]

Description

Terraform fails to read aws_iam_session_context data resource when you are running your Terraform code inside a private VPC in AWS as IAM has no service endpoint to attach:
https://docs.aws.amazon.com/vpc/latest/privatelink/aws-services-privatelink-support.html

Motivation and Context

Since KMS key creation and cluster admin permissions where this data resource referenced are conditional, we can use the same condition for aws_iam_session_context data resource.

Breaking Changes

Not a breaking change.

How Has This Been Tested?

• I have updated at least one of the examples/* to demonstrate and validate my change(s)
• I have tested and validated these changes using one or more of the provided examples/* projects
• I have executed pre-commit run -a on my pull request

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[bryantbiggs]

thank you!

[antonbabenko]

This PR is included in version 20.17.1 🎉

[jessebye]

This seems to break our EKS use:

╷
│ Error: Invalid index
│
│   on .terraform/modules/eks/main.tf line 151, in locals:
│  151:       principal_arn = data.aws_iam_session_context.current[0].issuer_arn
│     ├────────────────
│     │ data.aws_iam_session_context.current is empty tuple
│
│ The given key does not identify an element in this collection value: the collection has no elements.
╵
╷
│ Error: Invalid index
│
│   on .terraform/modules/eks/main.tf line 240, in module "kms":
│  240:   key_administrators        = coalescelist(var.kms_key_administrators, [data.aws_iam_session_context.current[0].issuer_arn])
│     ├────────────────
│     │ data.aws_iam_session_context.current is empty tuple
│
│ The given key does not identify an element in this collection value: the collection has no elements.
╵
error: Recipe `apply` failed on line 29 with exit code 1

I confirmed pinning the module to 20.16.0 resolves the issue.

[zacharyfleck]

I confirmed pinning the module to 20.16.0 resolves the issue.

Confirming the same. Felt a wave of panic briefly when I got the random error. 🤣 Thanks for the quick resolution though!

[bryantbiggs]

My apologies - we have reverted the commit

[zacharyfleck]

Thanks @bryantbiggs! Can also confirm all is good again with 20.17.2.

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