data staging: add `link` and `move` operations

[andre-merzky]

According to @SteVwonder, and reflected in the discussion here, data staging capabilities have been implemented as a prototype. It currently provides copy - I want to suggest to also add symlink and move semantics. In our experience, users often use data staging to have certain data located in specific locations, so that the application code can easily find them - but do not always need an actual copy. In those cases, link and move are much faster and can significantly reduce the load on the shared file system.

This is not really a feature request (we have that functionality covered in our own code), but a suggestion for further development. Thanks for you consideration :-)