Document the procedure for managing multiple accounts with AWS Single Sign-On

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Single Sign-On is an AWS service that makes it easy to create and manage AWS accounts under one root organization (which is responsible for paying the bill, a.k.a. consolidated billing).

This makes it possible to create and manage logically separate accounts for deploying the various instances (e.g., dev, staging and production), as well as environments for testing specific features or for developers to test their changes.

It makes sense to start a wiki page to document this process and keep it up to date.