cephfs: add checkContentSource() to validate the data source
cephfs: add checkContentSource() to validate the data source

checkContentSource() validate the data source in the request
and then populate volumeOptions or snapshotshot identifier in
case of snapshot source. If the data source is volume, then
parentVolumeOption and pvID are populated.

Signed-off-by: Humble Chirammal <dc8ba7e82a7df22725dedec9b10c7aaab9ec713f@redhat.com>

ceph/ceph-csi,ceph/ceph-csi,ceph/ceph-csi,ceph/ceph-csi