Publish multi arch[amd64/arm64] docker images for veneur

[code-haven]

Hello!

Would it be possible to publish an ARM64 compatible image for veneur? I couldn't find the build steps followed other than this readme: https://github.com/stripe/veneur/tree/master/public-docker-image. In the REAMDE, using docker buildx in place of docker build is all that's needed to publish a multi-arch build from my understanding.