single server docker image: pick your poison

Created by: uwedeportivo

addresses the single server issues (a fragile system with a lot of butterfly effects)

this didn't work https://github.com/sourcegraph/sourcegraph/pull/13107

also see https://github.com/sourcegraph/postgres-apk-builder https://github.com/sourcegraph/git-apk-builder

this upgrades the lot to alpine 3.12