Add network-tools to image streams

you need to add it here: https://github.com/openshift/cluster-samples-operator/blob/master/manifests/08-openshift-imagestreams.yaml and specify it in image references https://github.com/openshift/cluster-samples-operator/blob/master/manifests/image-references so it gets overriden with the ART image

To get image for specific release:
$ curl -s https://mirror.openshift.com/pub/openshift-v4/amd64/clients/ocp/4.11.8/release.txt | grep Pull
Pull From: quay.io/openshift-release-dev/ocp-release@sha256:6499bc69a0707fcad481c3cb73226c364586761c45b867dc31b345c6e6204e28

get a release image pullspec. Then a bit of a dance to verify that as a RH-signed release, in case hackers had compromized or man-in-the-middled the mirrors. And then:

$ oc adm release info --image-for network-tools quay.io/openshift-release-dev/ocp-release@sha256:6499bc69a0707fcad481c3cb73226c364586761c45b867dc31b345c6e6204e28
quay.io/openshift-release-dev/ocp-v4.0-art-dev@sha256:1091d1f2f3dae6d17e441044500e32a31984ae8ad236c2602e7ed1ba6af79b7c
And the customer knows they can trust 1091d1f2f3dae6d17e441044500e32a31984ae8ad236c2602e7ed1ba6af79b7c as the 4.11.8 network-tools, because they trusted the release image that referenced it.

Make sure to update user docs for disconnected clusters to get this image.