update generate_bulk_certificate_exceptions to DRF

[awais786]

Verify via postman

1. pass the url in postman using post.
2. upload the csv file. ( form-data: key= students_list and value = csvfile. )

expected result

{
    "general_errors": [],
    "row_errors": {
        "data_format_error": [],
        "user_not_exist": [],
        "user_already_allowlisted": [],
        "user_not_enrolled": [],
        "user_on_certificate_invalidation_list": []
    },
    "success": [
        "user \"admin\" in row# 1",
        "user \"awais_3\" in row# 2"
    ]
}

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Verify via instructor Dashboard

1. Open this Page
2. Go to Bulk Exceptions part and choose the file and press Add to exception list.

Expected result
It will show the message 2 learners were successfully added to exception list

demo csv file attached = students_list.csv

entries will appear in this table http://local.edly.io:8000/admin/certificates/certificateallowlist/