Done, but hasn't been tested yet to `mod-inventory-storage`. Might be that query has to be adapted

Don't forget to put a reference to the source record in the instance!
Or at least a corresponding ID for both (e.g. UUID).

Currently, mod-data-loader, when receiving a POST request on /load/marc-data, it will...

create a POST request that it submits to a storage URL (required param, see API) at /admin/importSQL.
This request consist of an SQL query with all (limited to the bulk size, if larger, multiple requests) records.

What I will probably do is add a second similar outgoing POST request for every current, containing the source strings (JSON) of the records. A corresponding table should be created in mod-inventory-storage.

Also, the API (POST /load/marc-data) of the mod-data-loader should be extended with a boolean that tells whether the source records should be stored.

As discussed in the back-end core team meeting, in the future, we might want to change the way the data loader interacts with the/a storage module, but not now.

Aside from this functionality I will probably add some small unit tests that check whether the SQL strings are created correctly. I will not continue to use the "test" API, as all current unit tests are implemented, but implement tests through the isTest==false path, to be able to test the whole code chain within the 'unit'. Forget this last remark if that might be confusing. It's the least important.