add "Mariner" for AKS os sku (Azure#20420)

Author: alexeldeib

specification/containerservice/resource-manager/Microsoft.ContainerService/preview/2022-08-02-preview/managedClusters.json

@@ -5363,6 +5363,7 @@
       "enum": [
         "Ubuntu",
         "CBLMariner",
+        "Mariner",
         "Windows2019",
         "Windows2022"
       ],