fix: encode the csv data before save

[arslanashraf7]

Description: Describe in a couple of sentences what this PR adds
This PR adds python's default(utf-8) encoding on the file data before saving.
This is not needed in the case of local storage while manipulating the grades but it becomes an issue when we use AWS/S3 storage as a backend instead of the local storage. The s3 services throw errors about file encoding.

A sample error log is attached below.

JIRA: Link to JIRA ticket
More details can be seen on mitodl/mitxonline#415

Dependencies: dependencies on other outstanding PRs, issues, etc.
None

Merge deadline: List merge deadline (if any)
No Specific Date but Soon

Installation instructions: List any non-trivial installation
instructions.

• Just set up the S3 backend storage for grades and then follow the instructions in open edx: Gradebook import grades functionality doesn't work mitodl/mitxonline#415 to reproduce and verify the fix.

Testing instructions:
Mentioned in mitodl/mitxonline#415

Sample Error Log
The sample error log can be seen:

2022-04-11 21:05:44,654 ERROR 7292 [root] [user None] [ip None] signals.py:22 - Uncaught exception from None
Traceback (most recent call last):
  File "/edx/app/edxapp/venvs/edxapp/lib/python3.8/site-packages/django/core/handlers/exception.py", line 47, in inner
    response = get_response(request)
  File "/edx/app/edxapp/venvs/edxapp/lib/python3.8/site-packages/django/core/handlers/base.py", line 181, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/usr/lib/python3.8/contextlib.py", line 75, in inner
    return func(*args, **kwds)
  File "/edx/app/edxapp/venvs/edxapp/lib/python3.8/site-packages/django/views/generic/base.py", line 70, in view
    return self.dispatch(request, *args, **kwargs)
  File "/edx/app/edxapp/venvs/edxapp/lib/python3.8/site-packages/bulk_grades/views.py", line 45, in dispatch
    return super().dispatch(request, course_id, *args, **kwargs)
  File "/edx/app/edxapp/venvs/edxapp/lib/python3.8/site-packages/django/views/generic/base.py", line 98, in dispatch
    return handler(request, *args, **kwargs)
  File "/edx/app/edxapp/venvs/edxapp/lib/python3.8/site-packages/bulk_grades/views.py", line 98, in post
    self.processor.process_file(the_file, autocommit=True)
  File "/edx/app/edxapp/venvs/edxapp/lib/python3.8/site-packages/super_csv/csv_processor.py", line 188, in process_file
    self.preprocess_file(reader)
  File "/edx/app/edxapp/venvs/edxapp/lib/python3.8/site-packages/bulk_grades/api.py", line 355, in preprocess_file
    self.save()
  File "/edx/app/edxapp/venvs/edxapp/lib/python3.8/site-packages/bulk_grades/api.py", line 333, in save
    return super().save(operating_user=self._user)
  File "/edx/app/edxapp/venvs/edxapp/lib/python3.8/site-packages/super_csv/mixins.py", line 118, in save
    operation = CSVOperation.record_operation(
  File "/edx/app/edxapp/venvs/edxapp/lib/python3.8/site-packages/super_csv/models.py", line 72, in record_operation
    instance.data.save(uuid.uuid4(), ContentFile(data))
  File "/edx/app/edxapp/venvs/edxapp/lib/python3.8/site-packages/django/db/models/fields/files.py", line 89, in save
    self.name = self.storage.save(name, content, max_length=self.field.max_length)
  File "/edx/app/edxapp/venvs/edxapp/lib/python3.8/site-packages/django/core/files/storage.py", line 54, in save
    name = self._save(name, content)
  File "/edx/app/edxapp/venvs/edxapp/lib/python3.8/site-packages/storages/backends/s3boto3.py", line 495, in _save
    self._save_content(obj, content, parameters=parameters)
  File "/edx/app/edxapp/venvs/edxapp/lib/python3.8/site-packages/storages/backends/s3boto3.py", line 510, in _save_content
    obj.upload_fileobj(content, ExtraArgs=put_parameters)
  File "/edx/app/edxapp/venvs/edxapp/lib/python3.8/site-packages/boto3/s3/inject.py", line 511, in object_upload_fileobj
    return self.meta.client.upload_fileobj(
  File "/edx/app/edxapp/venvs/edxapp/lib/python3.8/site-packages/boto3/s3/inject.py", line 431, in upload_fileobj
    return future.result()
  File "/edx/app/edxapp/venvs/edxapp/lib/python3.8/site-packages/s3transfer/futures.py", line 73, in result
    return self._coordinator.result()
  File "/edx/app/edxapp/venvs/edxapp/lib/python3.8/site-packages/s3transfer/futures.py", line 233, in result
    raise self._exception
  File "/edx/app/edxapp/venvs/edxapp/lib/python3.8/site-packages/s3transfer/tasks.py", line 126, in __call__
    return self._execute_main(kwargs)
  File "/edx/app/edxapp/venvs/edxapp/lib/python3.8/site-packages/s3transfer/tasks.py", line 150, in _execute_main
    return_value = self._main(**kwargs)
  File "/edx/app/edxapp/venvs/edxapp/lib/python3.8/site-packages/s3transfer/upload.py", line 692, in _main
    client.put_object(Bucket=bucket, Key=key, Body=body, **extra_args)
  File "/edx/app/edxapp/venvs/edxapp/lib/python3.8/site-packages/botocore/client.py", line 317, in _api_call
    return self._make_api_call(operation_name, kwargs)
  File "/edx/app/edxapp/venvs/edxapp/lib/python3.8/site-packages/botocore/client.py", line 591, in _make_api_call
    handler, event_response = self.meta.events.emit_until_response(
  File "/edx/app/edxapp/venvs/edxapp/lib/python3.8/site-packages/botocore/hooks.py", line 242, in emit_until_response
    responses = self._emit(event_name, kwargs, stop_on_response=True)
  File "/edx/app/edxapp/venvs/edxapp/lib/python3.8/site-packages/botocore/hooks.py", line 210, in _emit
    response = handler(**kwargs)
  File "/edx/app/edxapp/venvs/edxapp/lib/python3.8/site-packages/botocore/handlers.py", line 209, in conditionally_calculate_md5
    calculate_md5(params, **kwargs)
  File "/edx/app/edxapp/venvs/edxapp/lib/python3.8/site-packages/botocore/handlers.py", line 187, in calculate_md5
    binary_md5 = _calculate_md5_from_file(body)
  File "/edx/app/edxapp/venvs/edxapp/lib/python3.8/site-packages/botocore/handlers.py", line 201, in _calculate_md5_from_file
    md5.update(chunk)
TypeError: Unicode-objects must be encoded before hashing

Reviewers:

• tag reviewer
• tag reviewer

Merge checklist:

• All reviewers approved
• CI build is green
• Version bumped
• Changelog record added
• Documentation updated (not only docstrings)
• Commits are squashed

Post merge:

• Create a tag
• Check new version is pushed to PyPI after tag-triggered build is
  finished.
• Delete working branch (if not needed anymore)

Author concerns: List any concerns about this PR - inelegant
solutions, hacks, quick-and-dirty implementations, concerns about
migrations, etc.

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[natabene]

@arslanashraf7 Thank you for your contribution. Is this ready for our review?

[arslanashraf7]

@natabene Yes, it's ready for review.

[leangseu-edx]

LGTM

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