[Docs] Using Red Hat subscriptions in pipeline

Goal

Starting from OCP 4.9, Insights Operator is able to pull the customer's OCP entitlements and store them on the cluster as secrets:
https://docs.openshift.com/container-platform/4.9/support/remote_health_monitoring/insights-operator-simple-access.html

Furthermore, the Shared Resource CSI Driver enables admins to share a secret across multiple namespaces and mount it as a CSI volume in the pods:
https://issues.redhat.com/browse/BUILD-293
https://github.com/openshift/csi-driver-shared-resource

The goal of this epic is to document how the entitlements pulled by the Insights Operator could be used in a Pipeline to perform Dockerfile builds that install Red Hat rpms and thus require an entitlement. Furthermore, to elaborate how the Shared Resource CSI Driver could be used to mount those secrets using a CSI volume instead of duplicating the entitlement in every namespace that the pipeline needs to execute.

Acceptance Criteria

• Docs exist on how to perform entitled Dockerfile builds (installing Red Hat rpms) using the entitlement secret pulled by Insights Operator
• Docs exist on how to perform entitled Dockerfile builds (installing Red Hat rpms) using the Shared Resource CSI Driver in combination entitlement secret pulled by Insights Operator