Set the HTTP keep alive header for the FileManager.Import operation

It may be needed, at some point, to set the Connection: Keep-Alive header for when the FileManager.Import operation is called. I target this specific call because this is the only one that could last more than 6 minutes.
That is what seems to be recommended by Amazon. This is part of the NXDRIVE-2327 investigation but we tested and validated that just the TCP keep alive option is enough (NXDRIVE-2373).

I created the ticket "for later" and to not lose that part of the investigation.