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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


return crc32(to_bytes(response.content)) & 0xffffffff
def create_dynamodb_stream(data, latest_stream_label):
    stream = data['StreamSpecification']
    enabled = stream.get('StreamEnabled')
    if enabled not in [False, 'False']:
        table_name = data['TableName']
        view_type = stream['StreamViewType']
        dynamodbstreams_api.add_dynamodb_stream(
            table_name=table_name,
            latest_stream_label=latest_stream_label,
            view_type=view_type,
            enabled=enabled
        )
def forward_to_lambda(records):
    for record in records:
        sources = lambda_api.get_event_sources(source_arn=record['eventSourceARN'])
        event = {
            'Records': [record]
        }
        for src in sources:
            if src.get('State') != 'Enabled':
                continue
            lambda_api.run_lambda(func_arn=src['FunctionArn'], event=event, context={},
                asynchronous=not config.SYNCHRONOUS_DYNAMODB_EVENTS)
def forward_to_ddb_stream(records):