As an enhancement to https://github.com/localstack/localstack/pull/1194

It would be really helpful to send the Lambda name, either as data, a header, or as part of the URL.

At code location: https://github.com/localstack/localstack/blob/03c6f4bf250edd18eb818ed65090f508636b0bff/localstack/services/awslambda/lambda_api.py#L696

I can likely open a PR to handle this given some feedback on the feature and potential design.

Right now all I see is the following (using `npx http-echo-server`):
```
[socket#8] event: data
--> POST / HTTP/1.1
--> Host: 192.168.1.x:3000
--> User-Agent: python-requests/2.22.0
--> Accept-Encoding: gzip, deflate
--> Accept: */*
--> Connection: keep-alive
--> Content-Length: 9
--> Content-Type: application/x-www-form-urlencoded
-->
-->
[socket#8] event: data
--> Name=test
```
records.append(data)
                return 200
        records = []
        local_port = get_free_tcp_port()
        proxy = start_proxy(local_port, backend_url=None, update_listener=MyUpdateListener())
        items_before = len(records)
        _run_forward_to_fallback_url('%s://localhost:%s' % (get_service_protocol(), local_port))
        items_after = len(records)
        self.assertEqual(items_after, items_before + 3)
        proxy.stop()
    def test_dead_letter_queue(self):
        sqs_client = aws_stack.connect_to_service('sqs')
        lambda_client = aws_stack.connect_to_service('lambda')
        
        queue_name = 'test-%s' % short_uid()
        lambda_name = 'test-%s' % short_uid()
        queue_url = sqs_client.create_queue(QueueName=queue_name)['QueueUrl']
        queue_arn = aws_stack.sqs_queue_arn(queue_name)
        testutil.create_lambda_function(
            handler_file=TEST_LAMBDA_PYTHON, func_name=lambda_name, libs=TEST_LAMBDA_LIBS,
            runtime=LAMBDA_RUNTIME_PYTHON36, DeadLetterConfig={'TargetArn': queue_arn}
        )
        
        payload = {
            lambda_integration.MSG_BODY_RAISE_ERROR_FLAG: 1
        }
        lambda_client.invoke(FunctionName=lambda_name,
                             Payload=json.dumps(payload), InvocationType='Event')
        
        def receive_dlq():