The many datetime fields of videos (`created`, `startTime`, ...)

[LukasKalbertodt]

Also a discussion old as time: event metadata fields that contain datetimes and mean slightly different things. created, updated, startTime, endTime, bibliographical time, ... and more. (Note: while related, I will open a separate discussion issue for duration related stuff.)

TODO: someone needs to properly summarize the situation so far.

Previous discussions:

• Discuss: Event Metadata #1 (comment)
• Discuss: Event Metadata #1 (comment)
• Probably lots of old mailing list discussions that I cannot find right now... feel free to add.

[mtneug]

• Metadata: Start DateTime synchronizes with Created DateTime opencast#3473
• External API Metadata startDate and startTime opencast#3077
• Should Start DateTime be synchronized with Created DateTime?
• External Events API, need clarification about some fields
• New metadata field (long thread)