[C++] content-encoding field missing from s3 fs.

[adminy]

Describe the bug, including details regarding any error messages, version, and platform.

arrow/cpp/src/arrow/filesystem/s3fs.cc

Lines 1320 to 1324 in 1c15d13

	return {{"ACL", CannedACLSetter()},
	{"Cache-Control", StringSetter(&ObjectRequest::SetCacheControl)},
	{"Content-Type", ContentTypeSetter()},
	{"Content-Language", StringSetter(&ObjectRequest::SetContentLanguage)},
	{"Expires", DateTimeSetter(&ObjectRequest::SetExpires)}};

looking at the white listed cache keys here, I can see that there is no Content-Encoding header, only a content-type header.

Component(s)

C++

[alytantawyy]

take