Expose `SubjectGroup` as a column in participant-level results TSV

[alyssadai]

The API already returns subject_group as part of the "subject_data" key in the response object. The query tool should expose this information to the user as part of the participant-level downloads.

This way when users query for healthy controls, there is some explicit evidence (besides/in addition to their Diagnosis being empty) that the matched subjects are indeed healthy controls in our graph.

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[github-actions[bot]]

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