Remove the need for an external image registry for local development

[nwnt]

At the moment, the requirements for running the operator seem to suggest that we need an external image registry for the setup to work. Although I agree with this setup for Production, we don't really need the registry for local development.

Like I did here, we should be able to remove the need for external registry via:

• make docker-build without make docker-push
• For kind, we can upload the image with kind load docker-image. I believe other local kubenetes setup should also have mechanism to do the same thing.
• Setting imagePullPolicy: true for the operator (config/manager/manager.yaml). I just raised a PR for this (see Change imagePullPolicy to IfNotPresent #246).

Let me know if this makes sense for you guys. I can also add a documentation for local development if you want.