Return an array where each entry is an object with this form:

{ source: "fitbit", name: "Fitbit", usernames: ["beau", "madprime"] }

GET /api/public-data/members-by-source/?source=direct-sharing-252
HTTP 200 OK
Allow: GET, HEAD, OPTIONS
Cache-Control: max-age=0, no-cache, no-store, must-revalidate
Content-Type: application/json
Expires: Sun, 21 Jul 2019 06:20:19 GMT
Vary: Accept

{
    "count": 43,
    "next": null,
    "previous": null,
    "results": [
        {
            "source": "direct-sharing-252",
            "name": "nobism Ubiqum Cluster headache Project",
            "usernames": [
                "taximadman",
                "nobismRogierKoning",
                "Sara",
                "Pavia",
                "MarjoMontijn",
                "JST",
                "bright",
                "Valerian",
                "Romans8910",
                "Colinmunro3",
                "Deltaliam",
                "Ilja",
                "Coples79",
                "Joanfigueras",
                "sandiminar",
                "Deedee",
                "Jamesmill1987",
                "ruth1304",
                "Scott",
                "Leticiasierra87"
            ]
        }
    ]
}