S3 Object metadata keys are returned in lowercase

[ewbankkit]

Description

Following migration to AWS SDK for Go v2, S3 Object metadata keys are always returned in lowercase.
As the aws_s3_object and aws_s3_bucket_object resources have always required metadata keys to be lowercase (#1945), this only affects the aws_s3_object and aws_s3_bucket_object data sources querying objects created outside of Terraform.
Strictly speaking this is a breaking change but resolution would be complex and error prone.
Best to document and encourage practitioners to change configuration.

Relations

Closes #33648.
Relates #33358.
Relates #33593.

[github-actions]

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[YakDriver]

LGTM 🎉

[github-actions]

This functionality has been released in v5.19.0 of the Terraform AWS Provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

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[github-actions]

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