Use porscheinformatik image for openshift-route source example

[jgrumboe]

I would like to change the tutorial for openshift-route source to docker.io/porscheinformatik/external-dns, because I currently don't know when the images for registry.opensource.zalan.do/teapot/external-dns are built.

Furthermore it would be good to have images in an "official" kubernetes-sigs registry, if such exists.

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[jgrumboe]

Closing this one. Too many garbage from other commits. Sorry