update bulk_beta_modify_access api to DRF

[awais786]

Existing code

verify using postman

1. Post request using this URL

2. pass form-data

   identifiers: audit,awaisq
email_students: true
   auto_enroll: true
   action: add or remove

expected result

{
    "action": "add",
    "results": [
        {
            "identifier": "audit",
            "error": false,
            "userDoesNotExist": false,
            "is_active": true
        },
        {
            "identifier": "awaisq",
            "error": false,
            "userDoesNotExist": false,
            "is_active": true
        }
    ]
}

end to end testing

1. go to this page instructor > membership
2. pass valid usernames with comma separated e.g admin, staff
3. Press add beta testers button.
4. Now from below dropdown Select a course team role:: select beta testers.
5. It will load the admin and staff as beta testers.
6. Now repeat above steps 2 and press remove beta tester button.
7. Now from below dropdown Select a course team role:: select beta testers.
   8.It will appear empty.