Client: Set the "x-file-size" for binary uploads

[Jeeppler]

In #1471 we understood, that the S3 client requires the file length upfront. With #1551 we introduce the x-file-size header field for binary uploads.

This issue is about setting the x-file-size header in the client. The client needs to get the file size for binary files and set the x-file-size.

Depends on: #1551