eventbridge-sfn-terraform: Update AWS Provider to v6

[kakakakakku]

Issue #, if available:
N/A

Description of changes:
Hi😀 Thanks for the useful patterns!

To keep this pattern maintainable, I updated the AWS Provider to v6.

Check

terraform apply completed successfully and works good.

$ aws events put-events --entries file://event-A.json --region us-east-1
{
    "FailedEntryCount": 0,
    "Entries": [
        {
            "EventId": "c50fee9c-1316-0d0d-b8e1-e53d12c1289f"
        }
    ]
}

$ aws events put-events --entries file://event-B.json --region us-east-1
{
    "FailedEntryCount": 0,
    "Entries": [
        {
            "EventId": "5369ae64-7800-6347-1b6a-7a36d89b6c2a"
        }
    ]
}

$ aws events put-events --entries file://event-Fail.json --region us-east-1
{
    "FailedEntryCount": 0,
    "Entries": [
        {
            "EventId": "9710a0b6-a0bc-1471-28d6-1324da7c5bf5"
        }
    ]
}

Thank you😀

---

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[kakakakakku]

note: Fix to correct service name😀
https://docs.aws.amazon.com/step-functions/latest/dg/welcome.html

[parikhudit]

Naming: Request you to refer the official Lambda durable functions docs. Same applies in hitl-lambda-durable-function-cdk/README.md and fix pre-existing nits for AWS Service names, including this one.

[parikhudit]

@kakakakakku Thanks for the v6 bump and the service name fix.

[parikhudit]

Optional: jumping ~> 3.27 → ~> 6.0 skips v4 and v5. The Terraform v6 upgrade guide recommends stepping through the latest 5.x first. None of the resources used here seem to have v6 breaking changes, so for fresh deployments this works. However, please confirm in the PR description that you've run terraform init && terraform apply against ~> 6.0 end-to-end.
Thanks