Goal

Currently we have a lot of mixed code between U/s and D/s in the repository. Some code is not even used for either. 

This resulted as an outcome of migrating to a different build systems few times.

After this epic, the repository will only contain what is really needed. For example, we can remove the .kustomized_manifests which was deprecated in a favor of .down(up)stream_manifests files. Or we can remove the export-vars* scripts...

Please, take a look at the current state and what each thing does.

This should be done mainly in the operator/ directory, however there are leftover resources also in the root of the repo, e.g. PROJECT.

Upstream (U/s) build/s should follow the same build principle as D/s, e.g. it should utilize .upstream_manifests.

Also, we need to figure out a fix for operator-sdk not being able to generate relatedImages field in our CSVs for all active MTV versions and after that remove https://github.com/kubev2v/forklift/blob/release-2.9/operator/mtv-csv.yml (is currently only present on release-2.9 branch).