User can request a particular version of an LO

As a participant of the internet of logistics, I'd liek to be able to request a particular version of an LO via query parameter "at" in the GET-request for the LO.

Acceptance criteria

• If the "at" parameter is given, the API delivers the exact version of the LO at the given date/time.
• The date/time in the "at" parameter is provided in ISO-8601 format (without special characters like ":"). Example: YYYYMMDDThhmmssSSSZ