conda-forge k8s cloud builder

@mariusvniekerk did some work at SciPy 2019 on machinery to build an arbitrary feedstock given a kubernetes cluster. That work can be seen [here](https://github.com/mariusvniekerk/k8s-builder). I guess this issue is mostly to surface this work as a possible starting point for anyone else interested in this kind of capability. Possibly a blog post should come out of this once the work has moved forwards a bit.