upstream: require opt-in for the x-envoy-original-dst-host header. (#4046)
upstream: require opt-in for the x-envoy-original-dst-host header. (#4046)

*Risk Level*: Low
*Testing*: bazel test //test/...
*Docs Changes*: Added
*Release Notes*: Added

Signed-off-by: Piotr Sikora <piotrsikora@google.com>

Mirrored from https://github.com/envoyproxy/envoy @ 346059548e135199eb0b7f0006f3ef19e173bf79

lyft/envoy-api,lyft/envoy-api,lyft/envoy-api