Before this change, if an object compressed with "Content-Encoding:
gzip" was downloaded, a length and hash mismatch would occur since the
go runtime automatically decompressed the object on download, giving
errors like
corrupted on transfer: sizes differ
This change sets "Accept-Encoding: gzip" on all requests which stops
the go runtime decompressing objects on download, so compressed
objects are downloaded as-is with intact size and hash information.
If --oos-decompress is set then rclone will decompress objects with
"Content-Encoding: gzip" as they are received, at the cost of not
being able to check the length or the hash of the downloaded object.
Fixes#9694