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/package.json

@@ -2,7 +2,7 @@
   "name": "sql-migration",
   "displayName": "%displayName%",
   "description": "%description%",
-  "version": "0.0.11",
+  "version": "0.0.12",
   "publisher": "Microsoft",
   "preview": true,
   "license": "https://raw.githubusercontent.com/Microsoft/azuredatastudio/main/LICENSE.txt",
@@ -10,7 +10,7 @@
   "aiKey": "06ba2446-fa56-40aa-853a-26b73255b723",
   "engines": {
     "vscode": "*",
-    "azdata": ">=1.27.0"
+    "azdata": ">=1.29.0"
   },
   "activationEvents": [
     "onDashboardOpen",