v2.160.0

This release improves the proxy's error handling, introducing a new
`l5d-proxy-connection` header to signal from an inbound proxy when its
peers outbound connections should be torn down.

Furthermore, error handling has been improved so that the
`l5d-proxy-error` header is only sent to trusted peers--the inbound
proxy only emits this header when its client is meshed; and the outbound
proxy can be configured to disable these headers via configuration.