update list_report_downloads api upgrade to DRF

[awais786]

verify via postman

1. Try this URL in postman
2. Course Role should be set as data_researcher.
3. You need to waffle.flag as instructor.enable_data_download_v2.
4. select some option from the dropdown and press download report buttton.
5. It will download the file.

expected result
{ "downloads": [ { "name": "edx_cs222_2311_anonymized_ids_2024-08-22-1417.csv", "url": "/media/grades/73b48dc910e9bad3fb08a950770c499e1347501d/edx_cs222_2311_anonymized_ids_2024-08-22-1417.csv", "link": "<a href=\"/media/grades/73b48dc910e9bad3fb08a950770c499e1347501d/edx_cs222_2311_anonymized_ids_2024-08-22-1417.csv\">edx_cs222_2311_anonymized_ids_2024-08-22-1417.csv</a>" }, }

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