doc(backend_guide): add documentation for scaleway object storage as tfstate backend

[tcarecolin]

Hello, as a Scaleway user i encountered an issue when i attempted to use S3 backend not with AWS's3 but with Scaleway object-storage bucket
i had to find a workaround to make Scaleway credentials be correctly read by terraform

the issue is : by default Terraform backend S3 will read aws shared config file

~/$HOME/.aws/credentials

instead of using the correct scw config file

~/$HOME/.config/scw/config.yaml

i thought usefull for other people facing the same issue to complete the backend guide with a chatper on "S3 Backend"

[remyleone]

Hello, thanks for you contribution :) I think there are still many typos in the text could you take a look?

[tcarecolin]

Hello, thanks for you contribution :) I think there are still many typos in the text could you take a look?

done ✅

[Laure-di]

Hello @tcarecolin,

Thank you so much for your contribution!

The documentation for the S3 backend already exists here:
https://registry.terraform.io/providers/scaleway/scaleway/latest/docs#store-terraform-state-on-scaleway-s3-compatible-object-storage

That said, I completely agree that having backend-related information in multiple places — or worse, missing entirely from where users expect it — can be confusing. I’ll fix that by consolidating the content and adding more details about credential usage.

Thanks again for highlighting this!