Expose services configurations in a JSON endpoint

[leplatrem]

We could have an endpoint /services/{service} endpoint that returns the service configuration as JSON

Use-case:

• review current loaded configuration
• obtain service metadata. For example, if later if we want to have a reporting tool that sends a report via email to the services «managers», it could obtain the list of recipients from there.

Questions:

• how private are policies?
• should it be protected by Doorman? At nginx level?
• should it be a per-service configuration flag (public: true in yaml)