Remote storage backends don't support twine upload

[gerrod3]

When performing a twine upload to pulp_python using a remote storage backend like S3 the upload task will fail with the traceback:

pulpcore.tasking.pulpcore_worker:INFO:   File "/usr/local/lib/python3.9/site-packages/pulpcore/tasking/pulpcore_worker.py", line 268, in _perform_task
    result = func(*args, **kwargs)
 
  File "/usr/local/lib/python3.9/site-packages/pulp_python/app/tasks/upload.py", line 43, in upload
    content_to_add = pre_check or create_content(artifact_sha256, filename)
 
  File "/usr/local/lib/python3.9/site-packages/pulp_python/app/tasks/upload.py", line 105, in create_content
    shutil.copy2(artifact.file.path, temp_path)
 
  File "/usr/local/lib/python3.9/site-packages/django/db/models/fields/files.py", line 58, in path
    return self.storage.path(self.name)
 
  File "/usr/local/lib/python3.9/site-packages/django/core/files/storage.py", line 116, in path
    raise NotImplementedError("This backend doesn't support absolute paths.")