a field named "items" in InputObjectType occurs TypeError

I was trying to `json.dumps` with all inputs and some inputs had `TypeError` when they have a field named "items" like below.

```py
class ConfigInput(graphene.InputObjectType):
items = graphene.List(lambda: AnotherConfigInput)
...
```
when I try to `json.dumps` with this input, the error looks like
```py
File "/project/venv/lib/python3.7/site-packages/playhouse/mysql_ext.py", line 36, in db_value
return json.dumps(value)
File "/Users/user/.pyenv/versions/3.7.4/lib/python3.7/json/__init__.py", line 231, in dumps
return _default_encoder.encode(obj)
File "/Users/user/.pyenv/versions/3.7.4/lib/python3.7/json/encoder.py", line 199, in encode
chunks = self.iterencode(o, _one_shot=True)
File "/Users/user/.pyenv/versions/3.7.4/lib/python3.7/json/encoder.py", line 257, in iterencode
return _iterencode(o, 0)
TypeError: attribute of type 'list' is not callable
```

found that [`setattr` in `InputObjectType` class](https://github.com/graphql-python/graphene/blob/master/graphene/types/inputobjecttype.py#L23-L24) overrides field's attr `items` which conflicts with the attribute `items` of `List`.

This is naming conflict, so I just solved it like below
```py
class ConfigInput(graphene.InputObjectType):
_items = graphene.List(lambda: AnotherConfigInput, name='items')
...
```

wonder if there is any good fix from graphene like [this issue](https://github.com/graphql-python/graphene/issues/899)

please let me know if you need more info or examples :)

Start with the setattr logic in graphene/types/inputobjecttype.py at the linked lines and reproduce the conflict using an InputObjectType field named items. Determine how the field can retain its GraphQL name without breaking json.dumps, then verify the reported example no longer raises the TypeError.

Escrito por el modelo de indexación a partir del texto del issue.