Block public access for functions [AWS account level]

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**Description**
Allow customers to write policies to block public access for all functions in an account. Customers can specify at the account level whether to block the attachment of new policies that would allow public access and/or restrict access to functions that are currently publicly accessible. These controls will enable you to block new public policies form being attached to any function in an account without impacting functions that are currently publicly accessible.

En el issue no se identifican archivos, pruebas ni puntos de entrada. Empieza por aclarar los controles de las políticas de AWS Lambda a nivel de cuenta y si se requieren ambos comportamientos propuestos. Se considera completado cuando los clientes pueden bloquear nuevas políticas que permiten el acceso público y restringir opcionalmente las funciones que ya son accesibles públicamente.

Escrito por el modelo de indexación a partir del texto del issue.