Add missing Type to PluginCapability_VolumeExpansion

The PluginCapability_VolumeExpansion struct was missing a Type field to
indicate which type of volume expansion is supported. This commit fixes
that bug.

Signed-off-by: Jose A. Rivera <[email protected]>

Author: jarrpa

csi.proto

@@ -188,6 +188,7 @@ message PluginCapability {
       //   ControllerExpandVolume and NodeExpandVolume.
       OFFLINE = 2;
     }
+    Type type = 1;
   }
 
   oneof type {