[CLI] Take input for npm package name in all CLI generators with a default behaviour

まだ誰も着手していません。

## Feature proposal
Allow users to enter a npm package name for app and extensions. While they can still go change in package.json, there remains a doubt in user's mind if all required changes are done to change the package name. We can show a default suggestion based on the application or extension name after checking for valid package name. For a custom entered name, we still need to check for name validity.

## Current Behavior

Currently npm package name is auto generated based on the project name. This holds for both extensions and app.

## Expected Behavior

An extra option should come in CLI asking for a package name where users can choose to provide their scoped package names or any other name they want. Generator checks for the validity and shows a message if the package name is invalid. If everything is fine, it uses the provided name for npm package name.

まず、現在パッケージ名を導出している CLI ジェネレーターのコードを見つけ、app ジェネレーターと extension ジェネレーターのフローを比較します。両方のフローでオプションのパッケージ名を尋ね、有効なデフォルト値を提案し、カスタム入力を検証し、受け入れた名前を package.json で使用できれば完了です。

索引モデルが issue の本文から書いたものです。