[Improvement]: Add publishDate to objects and documents

[KatrinAckermannEk]

Improvement description

It would be beneficial to introduce an additional date type for objects and documents, specifically to indicate the initial publishing date by an editor.

Currently, the only available date fields for querying are modificationDate and creationDate. However, there are instances where an object or document is initially created as a draft, then published, and subsequently modified at a later stage. In such cases, it would be advantageous to be able to sort or query by the initial publishing date.