Allow to get all items when looking for sourceId and sourceItemId

[KlausIllmayer]

Currently, the API endpoint /api/sources/{sourceId}/item/{sourceItemId} queries against Solr. This means, we are not able to get results if the items are in the state INGESTED or SUGGESTED. But for the DACE ingestion we would need this feature. So when a user with the role system-contributor calls the endpoint, it should also deliver back the items that were ingested by this user (which is the ingestion pipeline).

Either the full API endpoint is changed so that it runs against the database and applies the authentication parameters, or a flag is introduced which allows to switch between a Solr call or a database + authentication call.

@tparkola Can you estimate which approach could be easier implemented.

If there are questions regarding the requirements by DACE please contact @ptylczynski