CI - Separate k8 image load from build script

[tjtelan]

Based on this comment https://github.com/infinyon/fluvio-connectors/issues/125#issuecomment-1024468529

The script we use for building and loading k8 images needs to be split up so we can re-use the loading script in other projects

This is the section I think needs to be factored out

https://github.com/infinyon/fluvio/blob/64bc5f11c46500aa3d05e352c2591f492ae69084/k8-util/docker/build.sh#L40-L58