Prometheus operator reference to master branch

The Prometheus Operator deploy section has a reference to a bundle.yaml file from the upstream repository [0], which is fragile because master branch is constantly evolved. There is a note about using the right OpenShift fork, which is exactly what we should provide. Something like [1] in case of OCP 4.4.

[0] https://raw.githubusercontent.com/coreos/prometheus-operator/master/bundle.yaml
[1] https://raw.githubusercontent.com/openshift/prometheus-operator/release-4.4/bundle.yaml