Test all possible data types that might exist in a graph

[alyssadai]

To ensure the API response is formatted correctly and without errors regardless of what the matching data looks like, we need tests that assert over the response given all possible graph database types allowed by Neurobagel, i.e. datasets with:
i. ONLY phenotypic data
ii. ONLY phenotypic + bids data (no derivatives)
iii. ONLY phenotypic + derivatives data (no BIDS)
iv. Phenotypic + bids + derivatives

• see datasets in https://github.com/neurobagel/neurobagel_examples/tree/main/data-upload
• this means either 1) spinning up multiple test graphs or 2) mocking these 4 types of graph responses
• we need to make sure the graph responses cover both aggregated and non-aggregated modes