Add support and documentation on how an application can control what info is returned in Decision API

As a Policy Designer, I want to be able to return information so that my application can more easily parse the Decision Response to get the properties my application needs for enforcement.

Most Decision applications return the full policy, while guard returns "permit" or "deny". Adding metadata can allow applications to fine-tune which properties to return for a decision.

This may also involve fine-tuning the Decision Request to turn on/off what is returned.

7/21/2021 - showing how to use obligations, advice and returning request attributes should be enough for this feature.