Ansible Plugin

To reproduce:

1. build a collecton to upload. I use the default one from mazer "here":
2. Upload it once. I use: http --form POST :24817/ansible/collections/ file@greetings_namespace-hello-11.11.11.tar.gz. Observe that works.
3. Upload it a second time and observe that you get a 500 error

Traceback (most recent call last):
  File "/usr/local/lib/pulp/lib64/python3.7/site-packages/django/core/handlers/exception.py", line 34, in inner
    response = get_response(request)
  File "/usr/local/lib/pulp/lib64/python3.7/site-packages/django/core/handlers/base.py", line 115, in _get_response
    response = self.process_exception_by_middleware(e, request)
  File "/usr/local/lib/pulp/lib64/python3.7/site-packages/django/core/handlers/base.py", line 113, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/usr/local/lib/pulp/lib64/python3.7/site-packages/django/views/decorators/csrf.py", line 54, in wrapped_view
    return view_func(*args, **kwargs)
  File "/usr/local/lib/pulp/lib64/python3.7/site-packages/rest_framework/viewsets.py", line 116, in view
    return self.dispatch(request, *args, **kwargs)
  File "/usr/local/lib/pulp/lib64/python3.7/site-packages/rest_framework/views.py", line 495, in dispatch
    response = self.handle_exception(exc)
  File "/usr/local/lib/pulp/lib64/python3.7/site-packages/rest_framework/views.py", line 455, in handle_exception
    self.raise_uncaught_exception(exc)
  File "/usr/local/lib/pulp/lib64/python3.7/site-packages/rest_framework/views.py", line 492, in dispatch
    response = handler(request, *args, **kwargs)
  File "/home/vagrant/devel/pulp_ansible/pulp_ansible/app/viewsets.py", line 216, in create
    artifact.save()
  File "/home/vagrant/devel/pulpcore/pulpcore/app/models/content.py", line 165, in save
    super().save(*args, **kwargs)
  File "/usr/local/lib/pulp/lib64/python3.7/site-packages/django/db/models/base.py", line 741, in save
    force_update=force_update, update_fields=update_fields)
  File "/usr/local/lib/pulp/lib64/python3.7/site-packages/django/db/models/base.py", line 779, in save_base
    force_update, using, update_fields,
  File "/usr/local/lib/pulp/lib64/python3.7/site-packages/django/db/models/base.py", line 870, in _save_table
    result = self._do_insert(cls._base_manager, using, fields, update_pk, raw)   
  File "/usr/local/lib/pulp/lib64/python3.7/site-packages/django/db/models/base.py", line 908, in _do_insert
    using=using, raw=raw)
  File "/usr/local/lib/pulp/lib64/python3.7/site-packages/django/db/models/manager.py", line 82, in manager_method
    return getattr(self.get_queryset(), name)(*args, **kwargs)
  File "/usr/local/lib/pulp/lib64/python3.7/site-packages/django/db/models/query.py", line 1186, in _insert
    return query.get_compiler(using=using).execute_sql(return_id)
  File "/usr/local/lib/pulp/lib64/python3.7/site-packages/django/db/models/sql/compiler.py", line 1335, in execute_sql
    cursor.execute(sql, params)
  File "/usr/local/lib/pulp/lib64/python3.7/site-packages/django/db/backends/utils.py", line 67, in execute
    return self._execute_with_wrappers(sql, params, many=False, executor=self._execute) 
  File "/usr/local/lib/pulp/lib64/python3.7/site-packages/django/db/backends/utils.py", line 76, in _execute_with_wrappers
    return executor(sql, params, many, context)
  File "/usr/local/lib/pulp/lib64/python3.7/site-packages/django/db/backends/utils.py", line 84, in _execute
    return self.cursor.execute(sql, params)
  File "/usr/local/lib/pulp/lib64/python3.7/site-packages/django/db/utils.py", line 89, in __exit__
    raise dj_exc_value.with_traceback(traceback) from exc_value
  File "/usr/local/lib/pulp/lib64/python3.7/site-packages/django/db/backends/utils.py", line 84, in _execute
    return self.cursor.execute(sql, params)
django.db.utils.IntegrityError: duplicate key value violates unique constraint "core_artifact_sha256_key"