Add HCOMisconfiguredDescheduler runbook

Signed-off-by: Simone Tiraboschi <stirabos@redhat.com>

docs/runbooks/HCOMisconfiguredDescheduler.md

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+# HCOMisconfiguredDescheduler
+
+## Meaning
+
+`Kube Descheduler Operator` is an optional operator, and it's not installed by
+default nor as a dependency of HCO.
+When installed it can work on a cluster with KubeVirt only if configured
+enabling `devEnableEvictionsInBackground` profileCustomization that
+is disabled by default.
+`DevEnableEvictionsInBackground` enables descheduler's EvictionsInBackground
+alpha feature.
+The EvictionsInBackground alpha feature is a subject to change.
+Currently provided as an experimental feature.
+
+## Impact
+
+If `Kube Descheduler Operator` is installed but not configured with
+`devEnableEvictionsInBackground` profileCustomization, `VirtualMachine`
+cannot be correctly managed by the descheduler.
+
+## Diagnosis
+
+1. Check the CR for `Kube Descheduler Operator`:
+
+   ```bash
+   $ kubectl get -n openshift-kube-descheduler-operator KubeDescheduler cluster -o yaml
+   ```
+
+looking for:
+
+   ```yaml
+   spec:
+      profileCustomizations:
+         devEnableEvictionsInBackground: true
+   ```
+
+If not there, the `Kube Descheduler Operator` is not correctly configured
+to work alongside KubeVirt.
+
+## Mitigation
+
+Set:
+   ```yaml
+   spec:
+      profileCustomizations:
+         devEnableEvictionsInBackground: true
+   ```
+on the CR for the `Kube Descheduler Operator`.
+Please notice that `EvictionsInBackground` is an alpha feature and it's subject
+to change and currently provided as an experimental feature.
+
+<!--DS: If you cannot resolve the issue, log in to the
+link:https://access.redhat.com[Customer Portal] and open a support case,
+attaching the artifacts gathered during the diagnosis procedure.-->
+<!--USstart-->
+If you cannot resolve the issue, see the following resources:
+
+- [OKD Help](https://www.okd.io/help/)
+- [#virtualization Slack channel](https://kubernetes.slack.com/channels/virtualization)
+<!--USend-->