ZeroMQ/zmq support

[iconoclasthero]

Describe the feature

Add ZeroMQ/zmq support.

I actually started looking at mpd > ffmpeg > zmq > ffplay > pulseaudio > alsa > speaker very early in my search for a network streaming solution to replace mpd > icecast > browser > pulseaudio > alsa > speaker. ffmpeg's libzmq implementation was broken and so I found MediaMtx and have been using it for the last 3-4 weeks.

The patch came through yesterday: https://trac.ffmpeg.org/ticket/11134 and it's been fantastic. I opened an ssh tunnel from behind t-moble cgnat (no public ip, no ports, no router control whatsoever) and it's just worked since then.

Seems to be a very solid protocol (in 12 hours of using it), low latency, uses websockets, seems pretty well suited for mediamtx actually.