DEICH-6106 - BIBBI Marc 21 - still disabled in prod + search source feature toggle

Added BIBBI 21 endpoint

As of now the endpoint will be disabled using feature toggle. One might invoke the source, but it will be filtered out, and no result is returned at all from this source.

As of now instead of BIBI21 the old, BIBI endpoint serves the clients with the old NORMARC format.

Note that a bug was found when moving over to MARC 21, which needs further investigation (https://jira.oslo.kommune.no/browse/DEICH-6167).

As the last commit message reads:

-For the BIBI21 endpoint one of the tests is somewhat fragile. Model isomorphism check fails for still not totally discovered reasons. However, BIBI21 is still disabled din prod, so the code might be merged in to master, and further work can be done to discover the reason of the problem.

Observations so far:

• seems like if the blank node ID reaches 1000, the model isomorphism check fails - which means that if the test case ("searchType": "TEXT","requests": [{"searchKind": "ALL","terms": ["M-065-11040-0"]) is moved further down in the searchTestSources.json file, it fails._
• if DeichModel.newIRI is run prior to code execution, the isomorphism check fails again_

The problem showed up after that the MARC21 format was introduced for the BIBI21 source. Apparently ALMA - which is using MARC21 as well - does not show these symptoms.

My current guess is that a combination of the data returned by BIBBI21 and how DeichModel is being built up causes the issue. Further investigation is needed.