backend/s3: Document need to reconfigure backend when updating Terraform

[gdavison]

Because of changes to the S3 Backend schema, some users are reporting that they need to reconfigure their backend when updating to Terraform 1.6, even if they have made no changes. Add this to the Upgrade Guide and S3 Backend documentation.

Relates #34022

Target Release

1.6.2

Draft CHANGELOG entry

Documentation change

[ghost]

@gdavison there's a typo on line 19 of website/docs/language/settings/backends/s3.mdx, and the same on line 142 of website/docs/language/upgrade-guides/index.mdx: "Becuase".

[mubarak-j]

should this example show backend S3 block?

terraform {
  backend "s3" {
    assume_role  {
        role_arn     = "arn:aws:iam::123456789012:role/example"
        session_name = "example-session"
        duration     = "15m"
    }
  }
}

[gdavison]

Yes, good catch

[jar-b]

LGTM 👍

[trujillo-adam]

Thanks for updating this information. I made some suggestions that are mostly around consistency with our style guide.

[gdavison]

Thanks to #34108, users do not need to reconfigure the backend. Leaving the deprecation documentation

[github-actions]

Reminder for the merging maintainer: if this is a user-visible change, please update the changelog on the appropriate release branch.

[github-actions]

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