Allow HTTPFuture callers to disable processing of "Content-Encoding" response headers
Summary: Ref T13507. In Phabricator, we perform a specific "Accept-Encoding: gzip" setup test and want to manually decode the result. Allow callers to disable handling of "Content-Encoding".
Test Plan: Ran all Phabricator setup checks.
Maniphest Tasks: T13507
Differential Revision: https://secure.phabricator.com/D21121