The CNO’s first holiday video has a soundtrack – and backup singers. Chief of Naval Operations Adm. Jon Greenert carols along with his wife Darleen, backed up by the 8-member a cappella group the Navy Sea Chanters in his holiday message, posted online Tuesday. “Happy holidays shipmates,” Greenert says above the cooing carolers. “We thank you and your families for your service and for your sacrifice and for those of you standing the watch tonight, remember what you do is incredibly important. You’re in our thoughts and prayers.” “Enjoy the holidays but please remember, stay safe,” Darleen adds. “Merry Christmas!” Greenert…