Proposal: change `GET /exchanges` to return a list of exchange IDs instead of a list of exchanges

[mistermoe]

This thought crossed my mind when considering how to support pagination for GET /exchanges and quickly realizing that it gets unwieldy quite fast. Without pagination we run the risk of returning massive response payloads. When attempting to include pagination, we can end up in situations where we may end up returning a portion of an exchange.

I think a better design might be to update GET /exchanges to return a list of exchange IDs instead of entire exchanges. GET /exchanges/:id can then be used to retrieve all of the messages for a given exchange

[phoebe-lew]

For end of Q1, spec text changes with solutions for:

• how would we do pagination with current GET /exchanges?
• how do we prevent GET /exchanges/:id from getting hammered if GET /exchanges just returns a list of IDs?