Use envoy as proxy

Status

proposed

Context

We need a proxy to handle outgoing requests. The usual runtime environment will be cloud-based, most probably with kubernetes as a cluster-manager.

Decision

The proxy to be used will be envoy.

Rational

is maintained by a wide community, most notably the CNCF, Lyft and Google.
is build for cloud purposes
very fast according to various benchmarks, thus limiting the impact on the broker performance
provides a lua-based scripting mechanism to add custom headers