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# Type of request: This is a ...

[ X ] bug report
[ ] feature request

# Detailed description

On BatchWriteItem if items are throttled, we are expected to receive a list of `UnprocessedItems` in the response instead of HTTP 500

## Expected behavior

Receive HTTP 200 but with Unprocessed Items in the response: https://docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_BatchWriteItem.html#DDB-BatchWriteItem-response-UnprocessedItems

## Actual behavior

Receive HTTP 500 ProvisionedThroughPutException. "All or nothing"

# Steps to reproduce

Start LocalStack with DynamoDb Service and "DYNAMODB_ERROR_PROBABILITY=1.0"

## Command used to start LocalStack

```
new LocalStackContainer(DockerImageName.parse("localstack/localstack:0.12.9"))
      .withEnv("DYNAMODB_ERROR_PROBABILITY", "1.0")
      .withServices(DYNAMODB)
```

## Client code (AWS SDK code snippet, or sequence of "awslocal" commands)

You can just Randomly generate a big list of objects (exceeding 1kb per batch) and check this behaviour


result = handle_special_request(method, path, data, headers)
        if result is not None:
            return result
        
        self.prepare_request_headers(headers)
        data_orig = data
        data = data or '{}'
        data = json.loads(to_str(data))
        ddb_client = aws_stack.connect_to_service('dynamodb')
        action = headers.get('X-Amz-Target', '')
        action = action.replace(ACTION_PREFIX, '')
        if self.should_throttle(action):
            return error_response_throughput()
        ProxyListenerDynamoDB.thread_local.existing_item = None
        if 'TableName' in data:
            table_def = TABLE_DEFINITIONS.get(data['TableName']) or {}
        if action == 'CreateTable':