Containerize docker-compose and unify usage

[legobeat]

There is already a custom docker-compose image built from a git submodule, due to the need for docker/compose#12032 for internal intracontainer (used only for GUI/X11 containers) usage.

• We use compose both inside and outside containers. We can use the same image for everything,
  • removing docker-compose as system dependency
  • allow using more recent features like silencing spurious warnings when running de
• In some environments the buildx-bake build takes some additional setup to get working
  • moving to upstream binary instead of compiling would remove this need
  • OTOH we could fix the build