update start_certificate_regeneration to DRF

[awais786]

Verify via postman

1. Try this URL as post.

it can take multiple params so you can pass following all also or any one.

pass form-data = 
    certificate_statuses: downloadable
    certificate_statuses: notpassing
    certificate_statuses: audit_passing
    certificate_statuses: audit_notpassing
    certificate_statuses: error

expected result

{
    "message": "Certificate regeneration task has been started. You can view the status of the generation task in the \"Pending Tasks\" section.",
    "success": true
}

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Verify via instructor dashboard

1. Open this page
2. Go to Student-Generated Certificates section.
3. Select options and press the Regenerate button.