Migrate jenkins job configs to pipelines

As part of the migration to the new Jenkins, instead of blindly creating a new jenkins job for push-latest-containers-to-quay_2.5 and rebuild-all-rhpkg-container-builds_2.5, let's turn them into a Jenkinsfiles first so they'll be more easily reused on the new server.

That way we can also have rebuild-all-rhpkg-container-builds_2.5 wait until all its triggered subtasks are done, and return an overall status... rather than just blindly triggering n jobs with no tracking/waiting.

We should also replace push-latest-containers-to-quay_2.5 with a wrapper that calls push-container-to-quay n times, and we could then turn push-container-to-quay into a Jenkinsfile too.

And then we can also replace get-sources-rhpkg-container-build with a jenkinsfile.

So that's 4 jobs to fix/migrate to pipelines:

• push-latest-containers-to-quay_2.5 & push-container-to-quay --> push-latest-container-to-quay
• rebuild-all-rhpkg-container-builds_2.4 --> ?
• get-sources-rhpkg-container-build --> ?

I suppose we can store these jenkinsfiles under https://github.com/redhat-developer/codeready-workspaces/tree/crw-2.5-rhel-8 ...

maybe under a new folder for "jenkinsfiles" or "build" ?

Right now we have jenkinsfiles in:

• ./ (server build)
• ./dependencies/ (che project builds like jwtproxy, machineexec, registries, pluginbrokers, etc., and update-digests.Jenkinsfile + send-email-qe-build-list.Jenkinsfile)
• ./product/ (bootstrapping a new release, eg., updateVersionAndRegistryTags.Jenkinsfile)

So... maybe we should reorganize things a bit? Ultimately I guess they're all moving to https://gitlab.cee.redhat.com/codeready-workspaces/crw-jenkins but we should settle on a dir structure that makes sense.