Add alert CDIMultipleDefaultVirtStorageClasses

docs/runbooks/CDIMultipleDefaultVirtStorageClasses.md

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+# CDIMultipleDefaultVirtStorageClasses
+<!-- Edited by akalenyu, 10 Oct 2023 -->
+
+## Meaning
+
+This alert fires when more than one default virtualization storage class exists.
+
+A default virtualization storage class has precedence over a default Kubernetes storage class for creating a VirtualMachine disk image.
+
+## Impact
+
+If more than one default virtualization storage class exists, a data volume that requests a default storage class (storage class not explicitly specified), receives the most recently created one.
+
+## Diagnosis
+
+Obtain a list of default virtualization storage classes by running the following command:
+
+```bash
+$ kubectl get sc -o json | jq '.items[].metadata|select(.annotations."storageclass.kubevirt.io/is-default-virt-class"=="true")|.name'
+```
+
+## Mitigation
+
+Ensure that only one storage class has the default virtualization storage class annotation.
+
+<!--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-->