Extend 403 template to request access

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Next step in the interaction:
Offer an input (button or whatever) to the user to make a request to access the resource.

There can be a number of ways to that.. config setting that shows the request form on all 403s and sends a notification to an (dedicated?) inbox, and/or if the resource has a dedicated inbox....

I said template in the title of this issue, but it'll act more like its own application (so that the server is not expected to process it like an HTML form) that sends a notification.

まず、現在の403テンプレートと、それを生成する認可パスを特定します。リクエストフローを選択する前に、サーバーがログイン中のユーザー、対象リソース、専用の受信トレイ（存在する場合）をどのように識別しているかを確認します。権限のないユーザーがアクセス要求を送信でき、意図した受信者が通知を受け取れる状態になれば完了ですが、payload によって設定と通知設計は未確定のままです。