Add an optional boolean flag to CMOs definition of RemoteWriteSpec that if true adds an entry in the specs WriteRelabelConfigs list.

I went with adding the relabel config to all user-supplied remote_write configurations. This path has no risk for backwards compatibility (unless users use the {}tmp_openshift_cluster_id{} label, seems unlikely) and reduces overall complexity, as well as documentation complexity.

The entry should look like what is already added to the telemetry remote write config and it should be added as the first entry in the list, before any user supplied relabel configs.