Bug 34054: Allow to embed biblio on GET /items

Bug 34054: Allow to embed biblio on GET /items

Test plan:
Request the /items REST API endpoint and ask for the biblio's info to be
embeded into the response passing x-koha-embed

curl -u koha:koha --request GET 'http://localhost:8081/api/v1/items' --header "x-koha-embed: biblio" --header "Content-Type: application/json"

Sponsored-by: BULAC - http://www.bulac.fr/
Signed-off-by: Andreas Roussos <a.roussos@dataly.gr>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>