arm64 production docker image build

[az5he6ch]

Pitch

I've tried building a Docker image myself from the docs in the wiki but haven't had much success in convincing it to actually run properly. It wasn't enormously clear what config was affecting what and how to convince it that it should be a prod environment rather than dev. Much more recently I noticed you were already building production Docker images. Having an image we can just run greatly simplifies self-hosting.

Motivation

The host I'm intending to self-host on is arm64 (free tier Oracle Cloud includes a fairly generous amount of Ampere compute).