Highlight a children element on a specific parent

This is needed for search v2 & different projects, see https://gitlab.com/arkindex/requests/-/issues/100

The element display should support a query parameter ?highlight=UUID where the UUID would the ID of a children element (a text line would be highlighted on the parent).

The parents of the highlighted element should also be requested in parallel, to be able to build the children tree all the way to the parent