Migration extension UX update and bug fixes. (#15384)

* Adding a null check to prevent infinite next button loading on account selection page.

* Remove a useless validation in migration cutover page

* Fixed some component formatting in source selection page

* Completely updated target selection page UX according to latest figma mockup

* Adding confirmation for migration cutover and cancel

* migration vbump

* azdata vbump in migration extension

* letting users do a cutover with unrestored files

* Fixing some localized strings

* Adding readme file for migration extension.

* Adding a static link for readme gif

* added sql mi typing, localized strings, some null checks

* casting target instance as sql mi

extensions/sql-migration/README.md

@@ -0,0 +1,30 @@
+# Azure SQL Migration
+Azure SQL Migration extension can be used to determine readiness of your SQL Server instances, identify a recommended Azure SQL target, and complete the migration of your SQL Server instance to Azure SQL Managed Instance or SQL Server on Azure Virtual Machine.
+
+## Installation
+From Azure Data Studio extension gallery, install the latest version of “Azure SQL Migration” extension and launch the wizard as shown below.
+
+![migration-animation](https://github.com/microsoft/azuredatastudio/blob/main/extensions/sql-migration/images/ADSMigration.gif)
+
+
+## Things you need before starting Azure SQL migration
+- Azure account details
+- Azure SQL Managed Instance or SQL Server on Azure Virtual Machine
+- Backup location details
+
+## Getting started
+Refer to getting started document (https://aka.ms/ads-sql-migration) for detailed documentation on capabilities and current limitations.
+
+## Need assistance or have questions/feedback
+Please reach out to DMSFeedback@microsoft.com
+
+
+## Code of Conduct
+This project has adopted the [Microsoft Open Source Code of Conduct](https://opensource.microsoft.com/codeofconduct/). For more information see the [Code of Conduct FAQ](https://opensource.microsoft.com/codeofconduct/faq/) or contact [opencode@microsoft.com](mailto:opencode@microsoft.com) with any additional questions or comments.
+
+## Privacy Statement
+The [Microsoft Enterprise and Developer Privacy Statement](https://privacy.microsoft.com/en-us/privacystatement) describes the privacy statement of this software.
+
+## License
+Copyright (c) Microsoft Corporation. All rights reserved.
+Licensed under the [Source EULA](https://raw.githubusercontent.com/Microsoft/azuredatastudio/main/LICENSE.txt).