Add support for passing %(duration)s to --sleep parameters

[JarLob]

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In order to not get banned it would be logical to sleep for the duration of the last downloaded video in a playlist. There is already support for duration in Output Template, but it doesn't work when passed to --sleep-interval.
Please implement something similar to:

1. "--sleep-interval %(duration)s"
2. "--sleep-interval %(duration)s --max-sleep-interval %(duration + 123)s" The idea is to sleep exactly how long the video lasts or a bit longer.

[dstftw]

1. duration is optional and may not be present.
2. Output template does not support any calculations.
3. Sleeping for duration time after downloading the whole file immediately does not make much sense since it still does not mimic webplayer behavior and easily detectable. Rate limiting download to video bitrate is more reasonable in this case.

[JarLob]

1. Presence of "duration" is specific to extractor, same as a chance to get a Ban. Pluralsight, for example. I know there is a duration implemented in the extractor and I know there is a chance to be banned. So it would work for specific extractors.
2. The second example with calculations was a "nice to have". At least feature 1. that doesn't require calculations could have been implemented.
3. I'm new to youtube-dl. Could you provide an example what parameters to pass to stay least detectable? What to pass to youtube-dl to limit download rate to the video bitrate automatically?