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
```
context = data_after['context']
        self.assertEqual('$LATEST', context['function_version'])
        self.assertEqual(lambda_name, context['function_name'])
        
        testutil.delete_lambda_function(lambda_name)
    def test_python_lambda_running_in_docker(self):
        if not use_docker():
            return
        testutil.create_lambda_function(
            handler_file=TEST_LAMBDA_PYTHON3, libs=TEST_LAMBDA_LIBS,
            func_name=TEST_LAMBDA_NAME_PY3, runtime=LAMBDA_RUNTIME_PYTHON36)
        result = self.lambda_client.invoke(
            FunctionName=TEST_LAMBDA_NAME_PY3, Payload=b'{}')
        result_data = result['Payload'].read()
        self.assertEqual(result['StatusCode'], 200)
        self.assertEqual(to_str(result_data).strip(), '{}')
        
        testutil.delete_lambda_function(TEST_LAMBDA_NAME_PY3)
    def test_handler_in_submodule(self):
        func_name = 'lambda-%s' % short_uid()
        zip_file = testutil.create_lambda_archive(
            load_file(TEST_LAMBDA_PYTHON), get_content=True,
            libs=TEST_LAMBDA_LIBS, runtime=LAMBDA_RUNTIME_PYTHON36,
            file_name='abc/def/main.py')
        testutil.create_lambda_function(func_name=func_name, zip_file=zip_file,
                                        handler='abc.def.main.handler', runtime=LAMBDA_RUNTIME_PYTHON36)
        
        result = self.lambda_client.invoke(FunctionName=func_name, Payload=b'{}')
        result_data = json.loads(result['Payload'].read())
        self.assertEqual(result['StatusCode'], 200)