Include scope information in the cds-services discovery endpoint

[dteirney]

During the connectathon, communicating the OAuth 2.0 scope that the CDS hook required involved some back and forth. The spec mentions this managed out-of-band when the EMR connects with a CDS Service. However, it could be beneficial if each hook in the discovery service could communicate the scope that it needs to get the necessary information from the FHIR server.

Specifying the scope for each hook may also help allow the access token provided by the CDS Client to include the needed scope for each hook. E.g. if one CDS hook needs read access but another needs write, a more constrained access token could be sent for the read-only hook.