Enable specification of the container engine for catalog builds

[trepel]

Overview

Makefile defines CONTAINER_ENGINE env var setting 'docker' as a default value. This env var should be used rather than having 'docker' hard-coded.

Verification Steps

make catalog-build
CONTAINER_ENGINE=docker make catalog-build
CONTAINER_ENGINE=podman make catalog-build

The output depends on your docker/podman config but if you have both installed and configured the commands should work. If you e.g. do not use docker then you can see something along the lines of
ERROR: Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?

[Boomatang]

Looks good to me, I don't have docker installed, but on main this failed to find docker when the env var was set. On this branch it worked.