User Documentation does not describe the usage of WorkloadResourceMapping

[pedjak]

Support for WorkloadResourceMapping was merged in #1086 but the user documentation does not mention it at all. Please keep the doc in sync with the available features, it took us quite some time to bring the doc to the current level, lets continue doing that.

[sadlerap]

There are still a few things missing from fully implementing support for ClusterWorkloadResourceMapping resources, namely:

• Correct rebinding when these resources are modified (semantics regarding this changed rather late in the spec stabilization process)
• Implementing validation webhooks for these resources
• Documenting this feature both here in our own documentation and downstream in openshift.

The intention was that #1086 was to implement most of the functionality needed to get support for these resources going, and split off some of the auxiliary things into separate pull requests. I felt that this was a better approach than implementing all of this as one big patch (which is rather difficult to review, can be risky, and would push back this feature even further).