It seems the Envoy apts have gone missing breaking out build, so instead of relying on the install let's docker compose their image as a proxy against the Redis supervisor instance as a simpler and faster-to-start setup that also works.

This rearranged some things to simplify the Docker story overall. A move to AzDO or just GitHub builds would simplify everything further, but we need to figure out Windows testing against a Docker setup in CI.