Adding Azure AD tenant dropdown in migration wizard (#14637)

* Added dropdown to select azure tenant in accounts page

* Added dropdown label for tenant dropdown

* Moving deepcopy to  utils
Exporting tenant type from azurecore

* Removing unnecessary stylings

* removing unnecessary async

extensions/sql-migration/src/api/utils.ts

@@ -0,0 +1,23 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the Source EULA. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+export function deepClone<T>(obj: T): T {
+	if (!obj || typeof obj !== 'object') {
+		return obj;
+	}
+	if (obj instanceof RegExp) {
+		// See https://github.com/Microsoft/TypeScript/issues/10990
+		return obj as any;
+	}
+	const result: any = Array.isArray(obj) ? [] : {};
+	Object.keys(<any>obj).forEach((key: string) => {
+		if ((<any>obj)[key] && typeof (<any>obj)[key] === 'object') {
+			result[key] = deepClone((<any>obj)[key]);
+		} else {
+			result[key] = (<any>obj)[key];
+		}
+	});
+	return result;
+}