Integrate generate script with task service (#426)

* Support generate script for backup

* change

* update task service data contract for Generate Script

* more changes

* update test

* add comments

* Add missing files

* update stub backup operation for testing

* pr comments

* remove empty space

* Fix tests

* Add unit/integration tests and isCancelable to TaskInfo

* address pr comments

* pr comments - fix tests

* fix minor issue

* fix minor issues

* remove unused variable

src/Microsoft.SqlTools.ServiceLayer/DisasterRecovery/DisasterRecoveryException.cs

@@ -0,0 +1,26 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+//
+
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace Microsoft.SqlTools.ServiceLayer.DisasterRecovery
+{
+
+    /// <summary>
+    /// Exception raised from disaster recovery operations
+    /// </summary>
+    internal sealed class DisasterRecoveryException : Exception
+    {
+        internal DisasterRecoveryException() : base()
+        {
+        }
+
+        internal DisasterRecoveryException(string m) : base(m)
+        {
+        }
+    }
+}