Modernize release pipeline and build multiarch images

[HappyTetrahedron]

Checklist

• Keep pull requests small so they can be easily reviewed.
• Categorize the PR by setting a good title and adding one of the labels:
  bug, enhancement, documentation, change, breaking, dependency, internal
  as they show up in the changelog

[HappyTetrahedron]

Unfortunately I think matrix strategy is not viable here, since buildx expects the entire multiarch image to be built in a single invocation (otherwise we'd have to do separate images) - unless there's some advanced stuff I'm not aware of, but I haven't found anything online.

[HappyTetrahedron]

Tested locally with:

commodore() {
  local pubring="${HOME}/.gnupg/pubring.kbx"
  if command -v gpgconf &>/dev/null && test -f "${pubring}"; then
    gpg_opts=(--volume "${pubring}:/app/.gnupg/pubring.kbx:ro" --volume "$(gpgconf --list-dir agent-extra-socket):/app/.gnupg/S.gpg-agent:ro")
  else
    gpg_opts=
  fi

  docker run \
    --interactive=true \
    --tty \
    --rm \
    --user="$(id -u)" \
    --env COMMODORE_API_URL=$COMMODORE_API_URL \
    --env COMMODORE_API_TOKEN=$COMMODORE_API_TOKEN \
    --env SSH_AUTH_SOCK=/tmp/ssh_agent.sock \
    --publish 18000:18000 \
    --volume "${SSH_AUTH_SOCK}:/tmp/ssh_agent.sock" \
    --volume "${HOME}/.ssh/config:/app/.ssh/config:ro" \
    --volume "${HOME}/.ssh/known_hosts:/app/.ssh/known_hosts:ro" \
    --volume "${HOME}/.gitconfig:/app/.gitconfig:ro" \
    --volume "${HOME}/.cache:/app/.cache" \
    ${gpg_opts[@]} \
    --volume "${PWD}:${PWD}" \
    --workdir "${PWD}" \
    ghcr.io/projectsyn/commodore:release-pipeline-update \
    $*
}

• works fine for me on amd64, to nobody's surprise

[HappyTetrahedron]

LMK if you'd prefer having autorelease on a separate PR

[simu]

LMK if you'd prefer having autorelease on a separate PR

I prefer not having autorelease at all for Commodore. Commodore has its own release process where release summaries are written manually as annotated tags.