Tde migration integration (#1806)

Adding certificate migration for encrypted databases.

Uses notifications to send events back to the client every time each database certificate is migrated.

src/Microsoft.SqlTools.ServiceLayer/Migration/Contracts/CertificateMigrationProgressEvent.cs

@@ -0,0 +1,44 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+//
+
+using Microsoft.SqlTools.Hosting.Protocol.Contracts;
+
+namespace Microsoft.SqlTools.ServiceLayer.Migration.Contracts
+{
+    /// <summary>
+    /// Parameters for the certificate migration progress event
+    /// </summary>
+    public class CertificateMigrationProgressParams
+    {
+        /// <summary>
+        /// Database name
+        /// </summary>
+        public string Name { get; set; }
+
+        /// <summary>
+        /// Message related to the success status. true should describe a positive outcome. false should have an error.
+        /// </summary>
+        public string Message { get; set; }
+
+        /// <summary>
+        /// Result of migration
+        /// </summary>
+        public bool Success { get; set; }
+    }
+
+
+    /// <summary>
+    /// Create a certificate migration request. This should be register at the client.
+    /// </summary>
+    public class CertificateMigrationProgressEvent
+    {
+        /// <summary>
+        /// Name and parameters for the event definition.
+        /// </summary>
+        public static readonly
+            EventType<CertificateMigrationProgressParams> Type =
+                EventType<CertificateMigrationProgressParams>.Create("migration/tdemigrationprogress");
+    }
+}