Just to get points on the board, this gives ImageUpdateAutomation an
`update` field into which you can plug the name of an ImagePolicy
resource (from the image reflector controller). The idea is that the
automation will then replace the image in the policy, anywhere it's
used, with its latest version.
This is enough to clone the repo that's referenced in the
ImageUpdateAutomation resource. It reproduces a bunch of code from the
source-controller which is internal there, to avoid writing it from
scratch.
Michael Bridgen