Docs feedback: How to configure distributed Runner cache with OpenShift

In configuration/configuring_runner_operator.md, we mention caching config items, but we have no coherent examples, like for example configuration/autoscale.md. It is however, clear that the latter is limited to executor = "docker+machine".

This leaves customers that use OpenShift and want a distributed cache with the choice of trying charts/gitlab/gitlab-runner/index.md, because it has Shared = true cache. But it's not clear whether that combination is possible.

In summary:

1. The OpenShift docs don't mention "distributed cache" but only cacheShared.
2. The k8S example doesn't mention "distributed" either, and neither "OpenShift".
3. The distributed cache docs don't mention "Kubernetes", nor "OpenShift".
4. Also, w have an explanation how the S3 URLs are structured in autoscale.md, but not in configuring_runner_operator.md.

A few clarifying sentences, and cross-links (if applicable) should be added, and/or a specific config example for OpenShift with cacheShared.

Related to #384121 (closed)