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-257
HTTP 200 OK
Allow: GET, HEAD, OPTIONS
Cache-Control: max-age=0, no-cache, no-store, must-revalidate
Content-Type: application/json
Expires: Wed, 04 Aug 2021 18:17:58 GMT
Vary: Accept

{
    "count": 53,
    "next": null,
    "previous": null,
    "results": [
        {
            "source": "direct-sharing-257",
            "name": "nobism reports for Advocating",
            "usernames": [
                "benc",
                "stephenbrad",
                "nobismRogierKoning",
                "Sara",
                "MarjoMontijn",
                "JST",
                "bright",
                "NabilNazir",
                "Scott",
                "Elly98",
                "Sven",
                "zawarski",
                "CatMargFras"
            ]
        }
    ]
}