Prevent registration of accounts under protected names

Certain account names like "security", "info", "admins", etc. shouldn't be registrable to avoid confusion. (That said, security has already been registered, by me as a sysadmin, to facilitate creation of the security-discuss mailing list. But sysadmins ought to be trusted not to misuse the name for other things, like posing security@ as a security contact address for the SRCF...)

Given that group account creation is subject to manual review, there is already a layer of prevention that should stop such names being taken. It would be better if the set of "reserved" account names is programmatically enforced by our systems, though.

まず、Python ライブラリ内のアカウントおよびグループ作成の経路を追跡し、名前が検証される箇所、または手動レビューが適用される箇所を特定します。既存のセキュリティアカウントの扱いを含め、保護された名前の動作を定義し、予約済みの名前を登録できない一方で、許可されたアカウントは引き続き機能することを示すテストを追加または更新します。