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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


record['dynamodb']['OldImage'] = existing_item
                record['dynamodb']['NewImage'] = updated_item
                record['dynamodb']['SizeBytes'] = len(json.dumps(updated_item))
                stream_spec = dynamodb_get_table_stream_specification(table_name=table_name)
                if stream_spec:
                    record['dynamodb']['StreamViewType'] = stream_spec['StreamViewType']
        elif action == 'BatchWriteItem':
            records = self.prepare_batch_write_item_records(record, data)
            for record in records:
                event_sources_or_streams_enabled = (event_sources_or_streams_enabled or
                    has_event_sources_or_streams_enabled(record['eventSourceARN'], streams_enabled_cache))
        elif action == 'TransactWriteItems':
            records = self.prepare_transact_write_item_records(record, data)
            for record in records:
                event_sources_or_streams_enabled = (event_sources_or_streams_enabled or
                    has_event_sources_or_streams_enabled(record['eventSourceARN'], streams_enabled_cache))
        elif action == 'PutItem':
            if response.status_code == 200:
                keys = dynamodb_extract_keys(item=data['Item'], table_name=table_name)
                if isinstance(keys, Response):
                    return keys
                
                if response._content == '{}':
                    response._content = update_put_item_response_content(data, response._content)
                    fix_headers_for_updated_response(response)
                if event_sources_or_streams_enabled:
                    existing_item = self._thread_local('existing_item')
                    
                    stream_spec = dynamodb_get_table_stream_specification(table_name=table_name)
                    record['eventName'] = 'INSERT' if not existing_item else 'MODIFY'