FEATURE: Private DataLink

[agy-why]

Daiquiri allows to provide access to private data via TAP. This feature is particularly important for research groups while developing a new catalog.

With the implementation of the datalink service, daiquiri is now able to provide a clean interface to serve related data, like fits files, previews...

This new feature has several advantage and would be very useful to research groups during the catalog development as well.
However, our implementation of datalink has only a public interface.

A solution would be to check user rights for a given ID before rendering the datalink table. This would add a access level for a given ID.

In order to achieve an access level within a given ID, would be much more complex, and is currently not necessary.