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.
Fixes#1398
The `x-amz-mp-object-size` request header can have two erroneous states: an invalid value or a negative integer. AWS returns different error descriptions for each case. This PR fixes the error description for the invalid header value case.
The invalid case can't be integration tested as SDK expects `int64` as the header value.
