A potential subscriber sends a TRACK_STATUS message on the control
stream to obtain information about the current status of a given track.
The TRACK_STATUS message format is identical to the SUBSCRIBE message (Section 9.7).
The receiver of a TRACK_STATUS message treats it identically as if it had received a SUBSCRIBE message, except it does not create downstream subscription state or send any Objects. Relays without an active subscription MAY forward TRACK_STATUS to one or more publishers, or MAY initiate a subscription (subject to authorization) as described in Section 8.4 to determine the response. The publisher does not send PUBLISH_DONE for this request, and the subscriber cannot send SUBSCRIBE_UPDATE or UNSUBSCRIBE.