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.

[github-actions]

We want to keep our issues up to date and active. This issue hasn't seen any activity in the last 75 days.
We have applied the _flag:stale label to indicate that this issue should be reviewed again.
When you review, please reread the spec and then apply one of these three options:

• prioritize: apply the flag:schedule label to suggest moving this issue into the backlog now
• close: if the issue is no longer relevant, explain why (give others a chance to reply) and then close.
• archive: sometimes an issue has important information or ideas but we won't work on it soon. In this case
  apply the someday label to show that this won't be prioritized. The stalebot will ignore issues with this
  label in the future. Use sparingly!