Support CONTAINER_ENGINE=(podman|nerdctl) in addition to docker

Dockerfile: Use long image names with the docker.io/ prefix for compatibility with Red Hat's containers
Dockerfile: Avoid using BuildKit features that are unsupported by buildah
docker-compose.yaml: Set the restart mode to always, as required by podman-restart.service
docker-compose.yaml: Remove tty: true, as it is unsupported by nerdctl compose up -d.
Makefile: Remove $(COMPOSE) cp, as it is unsupported by podman-compose

nerdctl support depends on:

rootless-containers / usernetes