helm: enable cephfs volume expansion by default

The cluster helm chart missed adding the default setting
for the volume expansion, so now we enable it by default.

Signed-off-by: Travis Nielsen <tnielsen@redhat.com>

cluster/charts/rook-ceph-cluster/values.yaml

@@ -375,6 +375,7 @@ cephFileSystems:
       isDefault: false
       name: ceph-filesystem
       reclaimPolicy: Delete
+      allowVolumeExpansion: true
       # see https://github.com/rook/rook/blob/master/Documentation/ceph-filesystem.md#provision-storage for available configuration
       parameters:
         # The secrets contain Ceph admin credentials.