Enable AWS client to copy objects >5GB in size

**Is your feature request related to a problem or challenge? Please describe what you are trying to do.**
I'm trying to copy objects within a bucket as part of my data ingestion workflow. However, when thse objects exceed 5GB in size, this fails with an error. There's a built-in limit in the S3 API for the maximum size of a copy operation.

**Describe the solution you'd like**

I've outlined the solution i'd prefer in #561 - essentially the copy method should detect large copies and transparently switch to a multipart workflow.

**Describe alternatives you've considered**

Alternatively, we could also expose this API as part of the multipart-upload API.

**Additional context**

Start by reading the existing copy method and the multipart-upload API, then review the approach outlined in issue #561. The work is done when copies over the S3 5GB limit transparently use a multipart workflow, or the API is exposed through multipart upload as decided by the implementation.

Written by the indexing model from the issue text.