* Add AWS IAM integration tests and refactor admin authorization
- Added AWS IAM management integration tests (User, AccessKey, Policy)
- Updated test framework to support IAM client creation with JWT/OIDC
- Refactored s3api authorization to be policy-driven for IAM actions
- Removed hardcoded role name checks for admin privileges
- Added new tests to GitHub Actions basic test matrix
* test(s3/iam): add UpdateUser and UpdateAccessKey tests and fix nil pointer dereference
* feat(s3api): add DeletePolicy and update tests with cleanup logic
* test(s3/iam): use t.Cleanup for managed policy deletion in CreatePolicy test
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