Create `destroyStreamingTicket` type call

Right now there is no way to cleanly close down a FFmpeg process and tell the server we have stopped watching. Therefor sessions are only cleaned after a 20 minute time-out or when you close down the server.

It would be nice if we were able to send a new mutation that tells the server we are done watching a certain piece of content and it's safe to clean-up any transcoding/muxing work that FFmpeg was working on and destroy the session.

The sessionID is already present when making the StreamingTicket so we should probably add that to the ticket as a new field and then accept a new mutation that will kill everything related to this session when it comes in.