Build Envoy and IO containers directly

This replaces Use Distroless Envoy images with a new decision to build IO container images directly using Google's distroless images and Envoy binaries that we build ourselves. Pros IO can use the latest features in Envoy, including prerelease versions. We can use a Debian 13 image , which is reportedly faster and has observably fewer security vulnerabilities. Cons We have to build our own Envoys, and Envoy builds are slow .