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
```
lambda_api.DO_USE_DOCKER = original_do_use_docker
    def test_lambda_subscribe_sns_topic(self):
        function_name = '{}-{}'.format(TEST_LAMBDA_FUNCTION_PREFIX, short_uid())
        testutil.create_lambda_function(handler_file=TEST_LAMBDA_ECHO_FILE,
                                        func_name=function_name, runtime=LAMBDA_RUNTIME_PYTHON36)
        topic = self.sns_client.create_topic(Name=TEST_SNS_TOPIC_NAME)
        topic_arn = topic['TopicArn']
        self.sns_client.subscribe(
            TopicArn=topic_arn,
            Protocol='lambda',
            Endpoint=lambda_api.func_arn(function_name),
        )
        subject = '[Subject] Test subject'
        message = 'Hello world.'
        self.sns_client.publish(
            TopicArn=topic_arn,
            Subject=subject,
            Message=message
        )
        events = get_lambda_log_events(function_name)
        self.assertEqual(len(events), 1)
        notification = events[0]['Records'][0]['Sns']
        self.assertIn('Subject', notification)
        self.assertEqual(notification['Subject'], subject)
    def test_lambda_send_message_to_sqs(self):
        function_name = '{}-{}'.format(TEST_LAMBDA_FUNCTION_PREFIX, short_uid())
        queue_name = 'lambda-queue-{}'.format(short_uid())
        sqs_client = aws_stack.connect_to_service('sqs')
        testutil.create_lambda_function(handler_file=TEST_LAMBDA_SEND_MESSAGE_FILE,
                                        func_name=function_name,