Items which are expected to be automatically downloaded don't

Files with a `Content-Disposition: attachment` are expected to be automatically saved by the browser.

This information is "lost-in-transition" currently (zimit1 and zimit2).

See https://github.com/openzim/zim-requests/issues/582#issuecomment-2139234144

To solve this issue we will definitely need custom headers processing (and storing inside the ZIM).