Add a reverse proxy VM between the client & server in the replay benchmarks

[dhess]

The reverse proxy VM (probably running nginx, traefik, or similar) will act as a sort of load balancer/TLS endpoint device and is a more realistic simulation of a production deployment. It will let us compare, e.g., compressed traffic delivered to the client vs uncompressed traffic delivered (by primer-service) to the load balancer.

[brprice]

In https://github.com/hackworthltd/primer/pull/837#issuecomment-1446216686, I wondered

Having both uncompressed and compressed stats would be useful, though perhaps they can be done in one benchmark, just by measuring either side of the proxy somehow (the current setup won't do that, as we only get tx/rx stats per interface; maybe setting up the proxy to have two interfaces: one for client, one for backend would work)

[dhess]

Yes, that will be easy: two networks, one for the client + proxy external interface, and one for the server + proxy internal interface.