test: implement s3 backend state in tests

[leiicamundi]

This PR leverage S3 backend as a tfstate storage. Related to https://github.com/camunda/team-infrastructure-experience/issues/306

For the reviewer, I'm unsure about the consequences of this implementation in the multiregion. (cc @Langleu)

[leiicamundi]

Thanks for pointing this out, @Langleu.

I’ve made the following changes:

• The backend configuration is now part of the fixtures, rather than the modules.
• The bucket is now created with a description. The region is included in the prefix since, even though the object is global, it's still tied to a region. The naming is purely for convenience.
• Since the bucket is statically referenced in the test configuration, I'll add it to our AWS IaC (https://github.com/camunda/infraex-terraform/pull/46).
• I created a cleanup script with an associated action to help remove resources from the bucket.
• The cleanup action is triggered in the CI tests in case of failure to ensure resource cleanup. Additionally, a scheduled workflow manages the removal of orphaned resources.

[Langleu]

I've disabled auto-merge for now.

[Langleu]

Overall, looks good! I think the only thing missing is alignment of the regions, as mentioned in https://github.com/camunda/infraex-terraform/pull/46 that the bucket would end up in eu-central-1 which isn't an issue but everything is built around a single AWS region. The only difference would be to have an input for the backend region vs execution region.