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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)
```


mapping = {}
    function_name = data['FunctionName']
    enabled = data.get('Enabled', True)
    batch_size = data.get('BatchSize')
    mapping['UUID'] = str(uuid.uuid4())
    mapping['FunctionArn'] = func_arn(function_name)
    mapping['LastProcessingResult'] = 'OK'
    mapping['StateTransitionReason'] = 'User action'
    mapping['LastModified'] = float(time.mktime(datetime.utcnow().timetuple()))
    mapping['State'] = 'Enabled' if enabled in [True, None] else 'Disabled'
    if 'SelfManagedEventSource' in data:
        source_arn = data['SourceAccessConfigurations'][0]['URI']
        mapping['SelfManagedEventSource'] = data['SelfManagedEventSource']
        mapping['Topics'] = data['Topics']
        mapping['SourceAccessConfigurations'] = data['SourceAccessConfigurations']
    else:
        source_arn = data['EventSourceArn']
        mapping['EventSourceArn'] = source_arn
        mapping['StartingPosition'] = LAMBDA_DEFAULT_STARTING_POSITION
    batch_size = check_batch_size_range(source_arn, batch_size)
    mapping['BatchSize'] = batch_size
    return mapping
def add_event_source(data):