Add requirements for low latency streaming use cases

[aboba]

This is an attempt to add requirements for low latency streaming use cases. The requirements for game streaming and other low latency streaming uses cases are somewhat different, so they each have their own section.

Partial fix for https://github.com/w3c/webrtc-nv-use-cases/issues/62

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[aboba]

@fippo PTAL.

[drkron]

Thanks @aboba! I think that this is a great initiative.

What do you think of adding another requirement regarding reduced jitter buffer on the receiving client?

[drkron]

The control of jitter buffer and rendering delay could be generalized to a Quality-of-Service API, where latency is traded for the perceived smoothness (dropped frames, freezes, etc).

[aboba]

@fippo @drkron Added the jitter buffer/rendering control requirements.

[aboba]

Comments from TPAC 2022:

1. For both use cases: RTCDataChannel in Workers.
2. For game streaming: Streaming input from GamePad via a worker.
3. For game streaming: Streaming input from AR/VR headsets (via RTP?).