This replaces prior logic where the :scheme header was consistently overwritten based on the encryption level of the upstream connection.
Risk Level: High (l7 change)
Testing: new integration tests, unit tests
Docs Changes: api docs updated
Release Notes: inline
Runtime guard: envoy.reloadable_features.preserve_downstream_scheme
Part of #14587
Signed-off-by: Alyssa Wilk <alyssar@chromium.org>
Mirrored from https://github.com/envoyproxy/envoy @ 8ac28e233538f0636b6e079f9d5569707b0ca815