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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)
```


region.lambdas.get(arn).aliases[alias] = new_alias
    return new_alias
def run_lambda(func_arn, event, context={}, version=None,
        suppress_output=False, asynchronous=False, callback=None):
    region_name = func_arn.split(':')[3]
    region = LambdaRegion.get(region_name)
    if suppress_output:
        stdout_ = sys.stdout
        stderr_ = sys.stderr
        stream = StringIO()
        sys.stdout = stream
        sys.stderr = stream
    try:
        func_arn = aws_stack.fix_arn(func_arn)
        func_details = region.lambdas.get(func_arn)
        if not func_details:
            LOG.debug('Unable to find details for Lambda %s in region %s' % (func_arn, region_name))
            result = not_found_error(msg='The resource specified in the request does not exist.')
            return lambda_executors.InvocationResult(result)
        
        invocation_type = 'Event' if asynchronous else 'RequestResponse'
        invoke_result = forward_to_external_url(func_details, event, context, invocation_type)
        if invoke_result is not None:
            return invoke_result
        context = LambdaContext(func_details, version, context)
        result = LAMBDA_EXECUTOR.execute(func_arn, func_details, event, context=context,
            version=version, asynchronous=asynchronous, callback=callback)
    except Exception as e:
        exc_type, exc_value, exc_traceback = sys.exc_info()
        response = {