(TK-10) Add get-registered-endpoints function with tests

I've added the get-registered-endpoints function to the service and have written some tests to go along with it. Whenever one of the service functions is called, a set in the state is updated with a map containing information on the endpoint and what created that endpoint. This set is then returned by the get-registered-endpoints function.
The wording in this docstring is a bit confusing.  Specifically, "A map of type ..."

I think it might make sense to just refer to the schemas in this docstring.  Perhaps something like "When the value of :type is :context, :endpoint will be an instance of ContextEndpoint".