Sync & transform upstream Che registries into CRW registries (filter out content, support multiarch container swaps for openj9)

See RHDEVDOCS-2483.

Sounds like we need to tweak the sync jobs for registries so that they pull content from upstream che-*registry repos.

Thus, still to do for 2.8:

• rhel.Dockerfile sync up -> mid [new transformation script] - CRW-1608
• transform synced code to exclude che-only things and add crw-only things (eg., remove che4z, add fuse and eap)
• push arch-aware transformation logic back upstream so we can switch from an openjdk sidecar to an openj9 one on the fly (needed for CRW on Z & P)

DONE for 2.7:

• build rhel.Dockerfile to collect artifacts [exists in Jenkinsfile already] : DONE - renamed from rhel.Dockerfile to Dockerfile and other Che-specific alpine Dockerfile + features in build.sh / readme were removed too.
• push tarballs to pkgs.devel [existed in Jenkinsfile already for 2.6, functionality moved to get-sources script ] : DONE
• transform upstream/midstream rhel.Dockerfile into brew.Dockerfile, push to crw-images GH repo [exists in Jenkinsfile already for devfile reg, but not plugin reg] : DONE, now in get-sources script for 2.7
• sync templates and other relevant files from upstream che registries -> https://github.com/redhat-developer/codeready-workspaces/tree/crw-2-rhel-8/dependencies/ --> should be a new sync*.sh script, like we have for operator, metadata, chectl: DONE
• sync mid-lower-stream (https://github.com/redhat-developer/codeready-workspaces-images/tree/crw-2.7-rhel-8/) to downstream pkgs.devel 1:1 sync using Kirk's sync-to-downstream job : DONE, including job rename from plugins-and-stacks