Simplify Kubernetes mode deployment

[rhuss]

The deployment for the Kubernetes mode is quite involved with a lot of moving parts (upload pods, persistent volumes, ..).

This can be drastically simplified with a technique described in https://github.com/rhuss/buildah-poc which uses an init-container for receiving the source code. This PoC uses buildah but could equally use Kaniko as well. The benefit of this approach are less things that can go wrong and that need to be cleaned up.