Simplify OpenShift cluster scaling instructions

https://gitlab.com/gitlab-org/cloud-native/gitlab-operator/-/blob/master/doc/developer/ci.md#scaling-openshift-clusters shows how to scale OpenShift clusters according to the Red Hat docs.

When launching a new cluster, I noticed that I could edit a machineset, editing the replicas from 1 to 2, and the new worker node came up without issue. The current section has multiple steps; we could replace it with something shorter like:

$ kubectl get machineset -n openshift-machine-api
ocp-ci-4717-78r9s-worker-a   2         2         2       2           2d1h
ocp-ci-4717-78r9s-worker-b   1         1         1       1           2d1h
ocp-ci-4717-78r9s-worker-c   0         0                             2d1h
ocp-ci-4717-78r9s-worker-f   0         0                             2d1h

$ kubectl -n openshift-machine-api scale --replicas=2 machineset/ocp-ci-4717-78r9s-worker-b
machineset.machine.openshift.io/ocp-ci-4717-78r9s-worker-b scaled