Fixes#1385
When accessing a specific object version, the user must have the `s3:GetObjectVersion` permission in the bucket policy. The `s3:GetObject` permission alone is not sufficient for a regular user to query object versions using `HeadObject`.
This PR fixes the issue and adds integration tests for both `HeadObject` and `GetObject`. It also includes cleanup in the integration tests by refactoring the creation of user S3 clients, and moves some test user data to the package level to avoid repetition across tests.
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