Inverted server connections

[alanconway]

Envoy can already make outbound HTTP client connections and accept inbound HTTP server connections.

AMQP is a bi-directional protocol: either end of a connection can send or receive messages. For envoy to act as a sidecar in an AMQP network, we want envoy to be able to "announce" itself as a message sink by making an AMQP client connection that acts as HTTP server connection that can receive incoming HTTP requests. For example we might have ephemeral envoy sidecars to connect to a well-known AMQP router to receive AMQP messages that are then forwarded as HTTP requests to local HTTP servers.