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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)
```


if (always_add_version or version != VERSION_LATEST) and len(result['FunctionArn'].split(':')) <= 7:
        result['FunctionArn'] += ':%s' % version
    return result
def forward_to_external_url(func_details, event, context, invocation_type):
    """ If LAMBDA_FORWARD_URL is configured, forward the invocation of this Lambda to the configured URL. """
    if not config.LAMBDA_FORWARD_URL:
        return
    func_name = func_details.name()
    url = '%s%s/functions/%s/invocations' % (config.LAMBDA_FORWARD_URL, PATH_ROOT, func_name)
    headers = aws_stack.mock_aws_request_headers('lambda')
    headers['X-Amz-Invocation-Type'] = invocation_type
    headers['X-Amz-Log-Type'] = 'Tail'
    client_context = context.get('client_context')
    if client_context:
        headers['X-Amz-Client-Context'] = client_context
    data = json.dumps(event) if isinstance(event, dict) else str(event)
    LOG.debug('Forwarding Lambda invocation to LAMBDA_FORWARD_URL: %s' % config.LAMBDA_FORWARD_URL)
    result = safe_requests.post(url, data, headers=headers)
    content = run_safe(lambda: to_str(result.content)) or result.content
    LOG.debug('Received result from external Lambda endpoint (status %s): %s' % (result.status_code, content))
    result = aws_responses.requests_to_flask_response(result)
    result = lambda_executors.InvocationResult(result)
    return result
def forward_to_fallback_url(func_arn, data):
    """ If LAMBDA_FALLBACK_URL is configured, forward the invocation of this non-existing
        Lambda to the configured URL. """
    if not config.LAMBDA_FALLBACK_URL:
        return
    lambda_name = aws_stack.lambda_function_name(func_arn)
    if config.LAMBDA_FALLBACK_URL.startswith('dynamodb://'):