feat(backup): support S3 advanced backup settings

[diegmonti]

Rollback Plan

If a change needs to be reverted, we will publish an updated version of the library.

Changes to Security Controls

No changes to security controls.

Description

• Allow aws_backup_plan advanced_backup_setting blocks to accept the S3 resource type.
• Document the S3 usage pattern in both Terraform and CDKTF guides.

Relations

• Relates r/aws_backup_plan: 'advanced_backup_setting.backup_options' and 'advanced_backup_setting.resource_type' are both Required #17692
• Relates r/aws_backup_plan: Add support for AdvancedBackupSettings #15341

References

• https://docs.aws.amazon.com/aws-backup/latest/devguide/API_AdvancedBackupSetting.html

Output from Acceptance Testing

% make testacc TESTS=TestAccBackupPlan_advancedBackupSetting PKG=backup
make: Verifying source code with gofmt...
==> Checking that code complies with gofmt requirements...
make: Running acceptance tests on branch: 🌿 f-advanced_backup_settings 🌿...
TF_ACC=1 go1.24.6 test ./internal/service/backup/... -v -count 1 -parallel 20 -run='TestAccBackupPlan_advancedBackupSetting'  -timeout 360m -vet=off
2025/09/26 11:16:46 Creating Terraform AWS Provider (SDKv2-style)...
2025/09/26 11:16:46 Initializing Terraform AWS Provider (SDKv2-style)...
=== RUN   TestAccBackupPlan_advancedBackupSetting
=== PAUSE TestAccBackupPlan_advancedBackupSetting
=== CONT  TestAccBackupPlan_advancedBackupSetting
--- PASS: TestAccBackupPlan_advancedBackupSetting (19.68s)
PASS
ok      github.com/hashicorp/terraform-provider-aws/internal/service/backup     19.777s

[github-actions]

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[github-actions]

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