Since the extended version is only available for amd64 I have started to
build Hugo on our own in a multi stage Dockerfile. Now we are installing
both binaries, regular hugo and extended hugo, bundled into the Docker
image.
Beside that the download for regular hugo and extended hugo should also
be more solid now.
After that I have also added more aliases for the environment variables.
As mentioned on some GitHub issue we are also installing more required
packages for a downloaded extended Hugo version as this relies on
libc6-compat and libstdc++.
