Downstream che-code container build process

Upstream che-code is coming along but the dockerfiles and build process are incompatible with Brew/OSBS in a number of ways:

• rpms from Fedora/EPEL (eg., libxkbfile, libsecret - libc.Dockerfile)
• yarn, node builds that don't vendor in advance for offline builds - libc.Dockerfile
• disparate arch support (eg., Chromium for x64 only, not Z or P - libc.Dockerfile)
  • Chromium not available from UBI8 or pulp RHEL8 content sets
• multiple dockerfiles instead of one multi-stage dockerfile
  • multiple FROMs - assembly.Dockerfile (this might be allowed by now in OSBS but there was a time where you could only have TWO stages for BUILD and RUNTIME)
  • inter-build dependency (puling machine exec executable from machine exec image) – would be potentially easier to store the executable in pkgs.devel lookaside cache than to try to pull from an OSBS internal build image (like we do for theia-dev -> theia or theia -> theia-endpoint) - assembly.Dockerfile
• dependency on DOCKER_BUILDKIT - probably not supported in Brew - readme