Please add `app.get_new_client()` to help with token rotation

From a discussion in #1324, the only safe way to call the client from outside a bolt handler when token rotation is on is to create a new client each time (as the handlers do)

Since Bolt is currently handling all of this for us, it'd be very useful to have a method along the lines of

client = await bolt.get_new_client(team_id)

that means callers do not need to deal with the InstallationStore and such themselves.

Category (place an x in each of the [ ])

• slack_bolt.App and/or its core components
• slack_bolt.async_app.AsyncApp and/or its core components
• Adapters in slack_bolt.adapter
• Others

Requirements

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まずディスカッション #1324 を確認し、その後、エントリーポイント slack_bolt.App と slack_bolt.async_app.AsyncApp、およびトークンローテーション中にそれらが InstallationStore をどのように使用するかを調査します。完了条件は、呼び出し側がストア自体を扱うことなく、要求されたメソッドを通じてチーム用に新しく作成されたクライアントを取得できることです。同期アプリと非同期アプリの両方が対象です。