Symphony Create a new real time messages / events stream ("datafeed").

_Available on Agent 2.57.0 and above._ The datafeed provides messages and events from all conversations that the user is in. The types of events surfaced in the datafeed can be found in the Real Time Events list. (see definition on top of the file) Returns the ID of the datafeed that has just been created. This ID should then be used as input to the Read Messages/Events Stream v4 endpoint.