Add Date uploaded and File duration to json --flat-playlist data

[optio50]

Checklist

• I'm reporting a feature request
• I've verified that I'm running youtube-dl version 2020.02.16
• I've searched the bugtracker for similar feature requests including closed ones

Description

Would like to have Date uploaded and File duration in json --flat-playlist data
It currently looks like this
{"url": "Oxz-n17BKVE", "_type": "url", "ie_key": "Youtube", "id": "Oxz-n17BKVE", "title": "Best Galaxy Z Flip features to try right away"}

I see there is an open and accepted request to support all get options but the upload or file date is not one of those.
#22493

[dstftw]

No such metadata is available. Nothing to do with #22493.

[optio50]

Sorry, I thought because meunierd specifically addressed this request on that "Issue" it was relevant.
YMMV
meunierd/youtube-dl@48829c4