Use Microsoft.Azure.RecoveryServices publisher for VM backup

Author: Kamran Khan

src/ResourceManager/Compute/Commands.Compute/Extension/AzureVMBackup/AzureVMBackupExtensionUtil.cs

@@ -38,8 +38,8 @@ namespace Microsoft.Azure.Commands.Compute.Extension.AzureVMBackup
     /// </summary>
     public class AzureVMBackupExtensionUtil
     {
-        public const string extensionPublisher = "Microsoft.OSTCExtensions";
-        public const string extensionType = "VMBackupForLinuxExtension";
+        public const string extensionPublisher = "Microsoft.Azure.RecoveryServices";
+        public const string extensionType = "VMSnapshotLinux";
         public const string extensionDefaultVersion = "0.1";
         public const string backupExtensionName = "vmbackupextension";
         public const string backupExtensionMetadataName = "vmbackuptag";