[ENH] Added Subject ID/Participant ID to JSON output file

[rmanaem]

Closes #477

Changes proposed in this pull request:

• Updated alterColumnCategoryMapping mutation to add the column mapped to Subject ID to the annotated data dictionary in the state
• Update getJSONOutput getter to add participant_id to the output file
• Expanded download-pagetests to check for identifies property and its value under participant_id key of the output file

Checklist

• PR has an interpretable title with a prefix ([ENH], [FIX], [REF], [TST], [CI], [MNT], [INF], [MODEL], [DOC]) (see https://neurobagel.org/contributing/pull_requests for more info)
• PR links to GitHub issue with mention Closes #XXXX
• Tests pass
• Checks pass

For new features:

• Tests have been added

For bug fixes:

• There is at least one test that would fail under the original bug conditions.

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[surchs]

Nice! I think that does it, @rmanaem!

🧑‍🍳