fix: replace deprecated bucket argument for recommended bucket_name

[mariajgrimaldi]

Description

The S3Boto3Storage backend no longer accepts the argument bucket. Use bucket_name or the setting AWS_STORAGE_BUCKET_NAME instead: jschneier/django-storages#636

This PR fixes this error in quince installations using django-storages 1.14:

  File "/openedx/edx-platform/./lms/envs/tutor/production.py", line 255, in scorm_xblock_storage
    return S3Boto3Storage(
  File "/openedx/venv/lib/python3.8/site-packages/storages/backends/s3.py", line 280, in __init__
    super().__init__(**settings)
  File "/openedx/venv/lib/python3.8/site-packages/storages/base.py", line 15, in __init__
    raise ImproperlyConfigured(
django.core.exceptions.ImproperlyConfigured: Invalid setting 'bucket' for S3Storage