ceph: write down the multipath support in the documents

OSD on PVC supports multipath thanks to the following commit.

ceph: add support for multipath devices
32730123ea

However, it's not documented yet.

Signed-off-by: Satoru Takeuchi <satoru.takeuchi@gmail.com>

Documentation/ceph-cluster-crd.md

@@ -312,7 +312,7 @@ The following are the settings for Storage Class Device Sets which can be config
 * `tuneSlowDeviceClass`: If `true`, because the OSD can be on a slow device class, Rook will adapt to that by tuning the OSD process. This will make Ceph perform better under that slow device.
 * `volumeClaimTemplates`: A list of PVC templates to use for provisioning the underlying storage devices.
   * `resources.requests.storage`: The desired capacity for the underlying storage devices.
-  * `storageClassName`: The StorageClass to provision PVCs from. Default would be to use the cluster-default StorageClass. This StorageClass should provide a raw block device or logical volume. Other types are not supported.
+  * `storageClassName`: The StorageClass to provision PVCs from. Default would be to use the cluster-default StorageClass. This StorageClass should provide a raw block device, multipath device, or logical volume. Other types are not supported.
   * `volumeMode`: The volume mode to be set for the PVC. Which should be Block
   * `accessModes`: The access mode for the PVC to be bound by OSD.
 

PendingReleaseNotes.md

@@ -22,6 +22,8 @@
 
 - rbd-mirror daemons that were deployed through the CephCluster CR won't be managed anymore as they have their own CRD now.
 To transition, you can inject the new rbd mirror CR with the desired `count` of daemons and delete the previously managed rbd mirror deployments manually.
+- OSD changes:
+  - OSD on PVC now supports multipath device.
 
 ## Known Issues