(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.
Would it be possible to combine these with your previous test?  I like that you are testing the alternate signatures, but it might be a little cleaner if we could just call some of the functions twice in the first test, since all of the setup is basically repeated.