This switches between storing chunks in a separate container suffixed
with `_segments` (the default) and a directory in the root
`.file-segments`)
By default the `.file-segments` mode will be auto selected if
`auth_url`s that require it are detected.
If the `.file-segments` mode is in use then rclone will omit that
directory from listings.
See: https://forum.rclone.org/t/blomp-unable-to-upload-5gb-files/42498/
5bf70c68f1