Resumable Upload: Add details about Transfer-Encoding and Content-Encoding

[Acconut]

With this PR, I attempt to clarify the role of content and transfer encoding in resumable upload that is:

• the bytes for offsets are counted on a representation, where Content-Encoding might be applied, but not Transfer-Encoding because that is a property of the transfer and not the representation itself.
• an upload retain the same content coding throughout its lifecycle, meaning that requests to resume the upload should target the same representation with the same content coding. Otherwise, data might end up invalid on the server if the content coding is switched during the upload.

Closes #2679 and #2674.