Add user roles / flags

[Syndesi]

Ticket is in early design phase.

Idea: Some advanced features should be restricted to individual groups, e.g. administrators. Furthermore if user defined rules are implemented in any capacity, then roles or flags directly attached to the user's object can help to short circuit rules without additional and expensive graph lookups.

Questions:

• Should the feature be named roles or flags? E.g. administrator and anonymousUser vs isAdmin and isAnonymous?
  It is likely that "roles" are more common for end users, and alternative wording can hinder adoption / onboarding.
• Which roles/flags should be defined by the system?
• Who can define new roles/flags?
• Endpoints for managing roles/flags?