Create endpoint for uploading data to the graph

[alyssadai]

We now have add_data_to_graph.sh that does most of the work of adding data to a graph:

https://github.com/neurobagel/api/blob/4ade1eb51a7f049fa4a57d1d7e36732b9ec94328/add_data_to_graph.sh

An API endpoint could do the same thing by receiving .jsonld files as a payload.

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