Support permissions on Storage Backends #209

Context
We've had some requests to be able to set permissions against Storage Backends. i.e. limiting which users have read/write/delete access on a given Storage Backend. We should explore adding this functionality, in the context of AppNote0016 fine-grained auth.

Description

• Explore how we might add permissions to Storage Backends
• Write up findings as an ADR
• Make changes to auth App Note as required
• Make changes to spec as required

Use Case
Restrict which users have read/write/delete access on specific Storage Backends