Add embargo information to the metadata

[jh-RLI]

Description of the issue

We are currently implementing the "EmbargoAre" in the OEP website. It makes sense to add this information to the Oemeta data if a table with embargo has been published.

Ideas of solution

• Introduction of a new field in the metadata "UnterEmbagroUntil".
• This field is set automatically as soon as the user selects the embargo time (during the publication of the data). It is also usabale outside the oep ecosystem of course.

Note: In future, users will be able to select the embargo option when uploading the data to the OEP. The data will then be available in "model_draf", but will not be publicly visible. The exact embargo time will only be selected when the user publishes the data via the OEP user interface or the API (and moves it from "model_draft" to another topic).

• Possibly another field like "isEmbargo" should also be added

Workflow checklist

• I am aware of the workflow in CONTRIBUTING.md