Publish an arm64 docker container image

[steve-forth]

The prebuilt binaries are available are built for both amd64 and arm64.
However the docker image on dockerhub is only published as amd64.

Would there be an appetite for both architecture types be published to docker hub?

[hfm]

#126 has been merged, so arm64 Docker images should be supported again starting with the next release.