Before this change, some files were giving this error when downloaded
from Cloudflare and other providers.
ERROR corrupted on transfer: sizes differ NNN vs MMM
This is because these providers auto gzips the object when rclone
wasn't expecting it to. (AWS does not gzip objects without their being
uploaded gzipped).
This patch adds a quirk to for fix the problem and a flag to control
it. The quirk `might_gzip` is set to `true` for all providers except
AWS.
See: https://forum.rclone.org/t/s3-error-corrupted-on-transfer-sizes-differ-nnn-vs-mmm/33694/Fixes: #6533