Docker builds should use the same binary as the goreleaser builds

[drewhammond]

This is fall out from the broken docker builds that were fixed recently. In order to get them working again, we started building the docker images on release "publish" actions. By the time this happens, Github has already built a set of binaries to attach to the release page.

There isn't a functional difference between the builds (at least not intentionally), but for security reasons we should ensure the binaries built into the docker image match the checksums of the binaries built for the release page.

Ideally this would all be handled in GoReleaser, but that's how I managed to break the docker builds in the first place 🙃