server: Build go binaries with Docker

Created by: keegancsmith

We still depend on the pre-build.sh step to generate assets / etc. But this gets us one step closer to just being able to docker build to generate an image.

The big downside I notice to this is whenever our go.mod file changes (somewhat regularly), we have to download all dependencies. I am guessing we can relatively easily work around this by getting an athens proxy involved.