provide single-yaml installation

[cirocosta]

Description of problem

Installing Cartographer is not as straightforward as it should be - rather than optimizing for the air-gapped case right of the bat, we should provide a simple installation method for those willing to fetch images from public repositories ala k apply -f <release.yaml>.

Proposed solution

For the current release, we could update it providing images coming from
DockerHub (projectcartographer) and point folks at installing from there.

I think we can achieve that with something like below:

gh release download v0.0.6 bundle.tar
imgpkg copy --tar bundle.tar --to-repo projectcartographer --lock-output lock.yaml
imgpkg pull --lock lock.yaml -o bundle
kbld -f ./bundle -f cartographer.yaml

Given that ultimately it's a matter of relocating to DockerHub and then making
the YAML available, that should do it.

For future releases though, we could update the releases scripts to have them
producing not only the bundle.tar, which can be relocated etc, but also a
cartographer.yaml file that points at DockerHub images.

[cirocosta]

done #200