Auto-build versions 10.5, 10.6, 10.11, 11.4, latest

Fixes: https://naturalis.atlassian.net/browse/AO-441

IMPORTANT! Do not merge this with main until the projects using the latest tag have been updated to use v10.5! It doesn't really matter if these images won't build temporarily, this is better than inadvertently upgrading to v11.4!

Setup mostly stolen from https://gitlab.com/naturalis/lib/docker/traefik. Includes 10.6 but can be removed if deemed unnecessary.

Note: excempted gosu from trivy scanning (cf Linnaeus repo), as this resulted in a large series of CVEs.