[Bug] - CopyObject should replace the Content-Type when copying with 'REPLACE' metadata directive

[niksis02]

Describe the bug
When attempting to copy an object with the REPLACE metadata directive, the Content-Type should be updated with the provided value: however, this does not occur in the gateway.

To Reproduce

// Create a bucket
aws s3api create-bucket --bucket tests

// Create an object
aws s3api put-object --bucket test --key my-obj --content-type audio/mp3

// Copy the object with REPLACE metadata directive
aws s3api copy-object --bucket test --key obj-copy --copy-source test/my-obj --content-type audio/mpeg --metadata-directive REPLACE

// Head object to see the copied result
aws s3api head-object --bucket test --key obj-copy

Expected behavior
The Content-Type should be replaced with the newly provided value.