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-468
HTTP 200 OK
Allow: GET, HEAD, OPTIONS
Cache-Control: max-age=0, no-cache, no-store, must-revalidate
Content-Type: application/json
Expires: Tue, 22 Sep 2020 04:10:23 GMT
Vary: Accept

{
    "count": 50,
    "next": null,
    "previous": null,
    "results": [
        {
            "source": "direct-sharing-468",
            "name": "OPEN",
            "usernames": [
                "gedankenstuecke",
                "stephenbrad",
                "246PWD",
                "MarcelZ",
                "swissalpine",
                "Unidragon",
                "Shaggydog",
                "steffen",
                "Jarvis532",
                "friendocrino",
                "markvader",
                "cristinav",
                "Shane",
                "chrisgruebl",
                "RalfCGM",
                "Lew_Easy",
                "jonmcalroy",
                "Pumpit",
                "guydavies",
                "Rachel162",
                "reimarmetzen",
                "Lispro",
                "RandomLuck",
                "MarkOldham",
                "Rainforest",
                "CGinDC",
                "jonprogers",
                "aholareijo",
                "kerray",
                "lopep",
                "ansku",
                "avitabile",
                "mohuma",
                "Cleo2014",
                "anirudhreddy28",
                "HermannW",
                "CaroGo",
                "Kz9Fl"
            ]
        }
    ]
}