[wip] Provide an alternate design for work package relations


See also discussion:
* https://github.com/opf/openproject/commit/91ba7ba6fba688dc61b09215ae39813e3a79149f
* https://www.openproject.org/work_packages/11676
* https://github.com/opf/openproject/pull/1542

In contrast to other links I can find in the documentation the links in this example do not have a "title".
Is that lazyness or intentional? (If it is the latter I don't see the intention ;-) )