Poll entity events

This is a long polling API that will first return all pre-existing data and then return all new data as it becomes available. If you want to start a new polling session then open a request with an empty 'sessionToken' in the request body. The server will return a new session token in the response. If you want to retrieve the next batch of results from an existing polling session then send the session token you received from the server in the request body. If no new data is available then the server will hold the connection open for up to 5 minutes. After the 5 minute timeout period, the server will close the connection with no results and you may resume polling with the same session token. If your session falls behind more than 3x the total number of entities in the environment, the server will terminate your session. In this case you must start a new session by sending a request with an empty session token.