Make osType a required field for HostGroup. (#15544)

Author: raazanand

mmv1/products/netapp/HostGroup.yaml

@@ -109,6 +109,7 @@ properties:
       used by all of the hosts in the HostGroup. All hosts in a HostGroup must be
       of the same OS type. This can be set only when creating a HostGroup.
     immutable: true
+    required: true
     enum_values:
       - 'LINUX'
       - 'WINDOWS'