Extends data in ndc-reference to capture a nested relationship

[daniel-chambers]

This PR extends the test data in ndc-reference so that it contains a nested relationship. This is useful for #183, but is being done separately in this PR so as to isolate the golden test changes that happen as a result of the test data change, but not as a result of changes in that RFC.

institutions gains a country_id under location, and a born_country_id for each staff member. These new fields link to a new countries collection. A new institution has also been added.

Other changes:

• The .json data files have been renamed to .jsonl to capture the fact that they are JSON Lines files, not JSON files
• The Int scalar type has had gt and lt comparison operators added to it

[daniel-chambers]

If we do that, I'd like to do it after all the current PRs are merged (which are all stacked on top of this one), since all the current tests rely on this specific data, and I'd rather rework the tests and their results in one go after the changes are in to keep it separate.