Add Containerfile, .containerignore, and Spindle CI/publish workflows (ci.yml and publish.yml) for building and publishing multi-arch (linux/amd64, linux/arm64) container images to atcr.io/sullen.net/harmony.
Containerfile&.containerignore: Multi-stagedenoland/deno:alpine-2.4.5build that pre-caches runtime modules and runsdeno task buildon$BUILDPLATFORMwith no target-archRUNsteps, defaulting toPORT=8080andHARMONY_DATA_DIR=/data.ci.yml: Runsdeno fmt --check,deno lint,deno task check,deno test, multi-archdocker buildx build, and an offline (--network none) HTTP smoke test against/about.publish.yml: Publishes:nightlyonmainpushes and:<tag>+:latestonv*tag pushes.