Add playoutDelayHint to webrtc receiver for smoother video playback

[mgroshans]

In general the idea is to alleviate stuttering that can occur even
without packet loss due to inconsistent packet timing by adding a small
buffer before playback.

This specific setting seems only partially supported and has changed
names several times. In the latest extensions spec[1], it is
defined as simply playoutDelay but only the slightly older name
playoutDelayHint property appears to have any effect on my testing for
Chrome 99.0.4844.51 on Windows 10. There appears to be an open issue to
add support for Firefox[2].

[1] https://w3c.github.io/webrtc-extensions/#rtcrtpreceiver-interface
[2] https://bugzilla.mozilla.org/show_bug.cgi?id=1592988

[mgroshans]

Since this adds latency it may be more desirable to make it optional or add it to the configuration, but I will leave that up to maintainers. I also think it's somewhat (but not wholly) redundant if GRVYDEV/Lightspeed-webrtc#30 is implemented.

And lastly I'll just emphasize that this will not fix all stuttering. Specifically it will only address stuttering that occurs even without packet loss; any stuttering caused by packet loss will remain.