[Docs] Test use of OpenShift Routes, document required settings
Summary
Context: #314 (comment 870449591)
We have some basic documentation on use of OpenShift Routes, but we should test that configuration and ensure we document all required values.
Specifically, with gitlab-org/charts/gitlab!2385 (merged) recently merged, we can set global.ingress.class=none
. This may be required for OpenShift's Router to pick up the Ingresses.