Docker arm64 support

[n0rdlicht]

As arm64 is advancing in the desktop and server worlds we should prepare the docker images to run natively.

Several issues are attached to this:

• switching to docker buildx for multi platform building
• postgis image seems to be unreliable for arm64 machines at the moment
• dynamic loading of S6 overlays depending on build platform inside Dockerfile
• dev experience: remote alpine arm64 containers in vscode are not yet working, see Build Alpine server for arm64 microsoft/vscode-remote-release#4462

PostGIS

In my case I switched to postgis/postgis:12-2.5-alpine, which seems to run fine. On other machines this was not the case and only a manual arm64 native build could get it working. postgis doesn't offer arm64 images yet, see postgis/docker-postgis#216.

Dynamic S6 Overlays

Could be solved by adding a small bash script as S6 uses different architecture abbreviates as either uname -mm or the Docker provided ARG TARGETARCH (see https://github.com/BretFisher/multi-platform-docker-build).

#!/bin/bash
if [ $(uname -mm) = "x86_64" ]
then
    S6_OVERLAY_ARCH=amd64
fi
if [ $(uname -mm) = "arm64" ]
then
    S6_OVERLAY_ARCH=arm64
fi
curl -Ls https://github.com/just-containers/s6-overlay/releases/download/$S6_OVERLAY_VERSION/s6-overlay-$S6_OVERLAY_ARCH.tar.gz | tar xz -C /

ADD s6_download.sh s6_download.sh
RUN sh s6_download.sh

Issues with postgis and vscode integration makes me wonder if we should wait until that becomes available or start offering arm64 images to have an easier transition in the future.

It would give the opportunity to simplify our image distribution process by switching to GitHubs Container Repository. I have already pushed test builds of both images and linked them to the repo, see https://github.com/orgs/cividi/packages?repo_name=spatial-data-package-platform. They are private for now and we would need to replace a couple of things in the Makefiles and docker-images.yml, but very doable and seems to be working well on my end.

@yvess whats your take here?