added source_url_explainer handling to search ui

This will add handling of the newly added source_url_explainer to the search-ui. We will display this field now if available and add a fallback for other cases of a generic landingpage before defaulting to the normal wording for direct links.

We will also copy relevant info for the user, in certain cases the ID or in other cases the title as a QOL improvement if the user has to use the search function on the landing page

See merge request !112