add embargo to work version form

[Smullz622]

Fixes #1486

Couple notes on this:

• Since the embargo form couldn't be used here, the validations are moved to the model level. Also, 'not a date' validations were no longer needed since the field was switched to a date picker instead of a string field. The date picker handles those validations automatically.
• Embargo section only shows up on v1 draft for work version and can be updated in work settings afterwards. Thought process was that we want to give users the ability to add embargo before publishing but don't want to give users the impression that they'll have to create a new work version in order to update embargo.
• This created a rails weird edge case where an invalid embargo date was rendering the 'maximum embargo is four years' error twice. There's a hacky work around for now that removes duplicate max embargo errors.