As a HyperShift operator
I want S3 operations migrated to AWS SDK v2
So that OIDC bucket management works correctly

Acceptance Criteria:

• [ ] Migrate S3 client in hostedcluster_controller.go
• [ ] Update etcd-backup S3 operations
• [ ] OIDC bucket creation/deletion works
• [ ] Bucket encryption and public access block configured correctly
• [ ] All S3 tests pass

Files:

• /hypershift-operator/controllers/hostedcluster/hostedcluster_controller.go
• /etcd-backup/etcdbackup.go
• /cmd/infra/aws/s3.go