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/azurecore/src/azureResource/azure-resource.d.ts

@@ -91,6 +91,32 @@ declare module 'azureResource' {
 		}
 
 		export interface AzureSqlManagedInstance extends AzureGraphResource {
+			sku: {
+				capacity: number;
+				family: string;
+				name: string;
+				tier: 'GeneralPurpose' | 'BusinessCritical';
+			},
+			properties: {
+				provisioningState: string,
+				storageAccountType: string,
+				maintenanceConfigurationId: string,
+				state: string,
+				licenseType: string,
+				zoneRedundant: false,
+				fullyQualifiedDomainName: string,
+				collation: string,
+				administratorLogin: string,
+				minimalTlsVersion: string,
+				subnetId: string,
+				publicDataEndpointEnabled: boolean,
+				storageSizeInGB: number,
+				timezoneId: string,
+				proxyOverride: string,
+				vCores: number,
+				dnsZone: string,
+			  }
+
 		}
 
 		export interface ManagedDatabase {