#50 Add option for initial recording date

What the feature will be:

• enabled by default
• force --no-originaldate to disable
• same date for peertube and youtube
• Try to guess the date from the video using metadata? (not easy to use see next comment) or file last modification?
• If not possible, use the upload date
• Possibility to overwrite the date by using originaldate=DATE

For youtube, the recordingDate is a datetime value: https://developers.google.com/youtube/v3/docs/videos?hl=fr#recordingDetails.recordingDate

Same than for publishAt, so we may reuse the conversion function.

For Peertube, we may use the originallyPublishedAt field: https://docs.joinpeertube.org/api-rest-reference.html#tag/Video/paths/~1videos~1upload/post

Unfortunately, it seems there is no normalized format for metadata on video, so the existence of creation time in metadata depends totally of the recording software.

For example, OBS does not add it:

$ ffmpeg -i somevideo.mp4 -dump
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'somevideo.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.29.100
  Duration: 00:37:40.63, start: 0.033000, bitrate: 4332 kb/s
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709), 1920x1080 [SAR 1:1 DAR 16:9], 4000 kb/s, 30 fps, 30 tbr, 90k tbn, 60 tbc (default)
    Metadata:
      handler_name    : VideoHandler
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 160 kb/s (default)
    Metadata:
      handler_name    : SoundHandler
    Stream #0:2(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 149 kb/s
    Metadata:
      handler_name    : SoundHandler
    Stream #0:3(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 3 kb/s
    Metadata:
      handler_name    : SoundHandler
    Stream #0:4(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 3 kb/s
    Metadata:
      handler_name    : SoundHandler

I'll backup to the file modification date instead, more reliable, even if it may be inexact. In this case, the manual option to overwrite could be used.