Landing page for hidden n/a data packages and elements nested withhin the data package

[AndyDaniel1]

In very rare cases it can happen that a data package is completely hidden / no longer available. Currently, the doi redirects to the latest version and a warning is displayed (see screenshot).

This is not sufficient as the doi of the datapackage and every element that is nested in the hidden version has no longer a unique landing page. Thus, in the future, we should set up a single landing page that displays basic metadata about the hidden data package. The data package doi of this version and any PID nested in this version of the data package should be redirected to this landing page. In the case of the implementation of #3303, this would mean that every variable PID is redirected to this single landing page. An alternative could be to implement n/a landing pages for every element, but this could be quite confusing for data users.

The n/a landing page(s) should have a prominent link to another version of the data package (if available).

If a complete data package, with multiple versions will become n/a every version should get a n/a landing page but with the hint that there is no available version.