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# Type of request: This is a ...

[x] bug report
[ ] feature request

# Detailed description
When I call the Lambda PutFunctionEventInvokeConfig API using the aws-java-sdk, the sdk throws an exception claiming it cannot parse the LastModified timestamp in the response:
```
software.amazon.awssdk.core.exception.SdkClientException: Unable to parse date : 2021-05-28T16:02:30.018Z
        at software.amazon.awssdk.core.exception.SdkClientException$BuilderImpl.build(SdkClientException.java:98)
        at software.amazon.awssdk.protocols.core.StringToInstant.lambda$safeParseDate$0(StringToInstant.java:77)
        at software.amazon.awssdk.protocols.core.StringToInstant.convert(StringToInstant.java:54)
        at software.amazon.awssdk.protocols.core.StringToInstant.convert(StringToInstant.java:32)
```

For comparison, the response for a getting a FunctionEventInvokeConfig for a Lambda of a real AWS account using the aws-cli is the following:
```
{
    "LastModified": "2021-05-27T19:26:43.454000-07:00",
    "FunctionArn": "...",
    ...
}
```

## Expected behavior
LambdaAsyncClient in aws-java-sdk should correctly parse the response for a PutFunctionEventInvokeConfig request.

## Actual behavior
LambdaAsyncClient in aws-java-sdk throws an exception when parsing the LastModified field in the response.

# Steps to reproduce

## Command used to start LocalStack
```
docker run -d --rm --name localstack -p 4566:4566 localstack/localstack:latest
```

## Client code (AWS SDK code snippet, or sequence of "awslocal" commands)
```
val putEventInvokeConfigRequest =
  PutFunctionEventInvokeConfigRequest.builder
    .functionName(functionName)
    .maximumEventAgeInSeconds(21600)
    .maximumRetryAttempts(0)
    .build
lambdaClient.putFunctionEventInvokeConfig(putEventInvokeConfigRequest)
```


return response_obj, details['StatusCode'], details['Headers']
    
    not_found = None
    region = LambdaRegion.get()
    if arn not in region.lambdas:
        not_found = not_found_error(arn)
    elif qualifier and not region.lambdas.get(arn).qualifier_exists(qualifier):
        not_found = not_found_error('{0}:{1}'.format(arn, qualifier))
    if not_found:
        try:
            forward_result = forward_to_fallback_url(arn, json.dumps(data))
            if forward_result is not None:
                return _create_response(forward_result)
        except Exception as e:
            LOG.debug('Unable to forward Lambda invocation to fallback URL: "%s" - %s' % (data, e))
        return not_found
    if invocation_type == 'RequestResponse':
        context = {'client_context': request.headers.get('X-Amz-Client-Context')}
        result = run_lambda(func_arn=arn, event=data, context=context, asynchronous=False, version=qualifier)
        return _create_response(result)
    elif invocation_type == 'Event':
        run_lambda(func_arn=arn, event=data, context={}, asynchronous=True, version=qualifier)
        return _create_response('', status_code=202)
    elif invocation_type == 'DryRun':
        
        return _create_response('', status_code=204)
    return error_response('Invocation type not one of: RequestResponse, Event or DryRun',
                          code=400, error_type='InvalidParameterValueException')
@app.route('%s/event-source-mappings/' % PATH_ROOT, methods=['GET'])
def get_event_source_mappings():