Endpoint to get subjects in a group

[mekhlakapoor]

Is your feature request related to a problem? Please describe.
As a user, I want to be able to pull metadata for all the mice in a group. Given a group ID, fetch a list of subject_ids from labtracks. Maybe then use the subject and procedure endpoints to fetch the metadata for these mice?

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[jtyoung84]

@saskiad Do you have any suggestions for this?