**Overview**

In AWS it is possible to trigger step functions through an API Gateway integration, see https://docs.aws.amazon.com/step-functions/latest/dg/tutorial-api-gateway.html

Similar integrations already occur within localstack, however the step function URIs are notably missing. See lines 66-88 of https://github.com/localstack/localstack/blob/master/localstack/services/apigateway/apigateway_listener.py



┆Issue is synchronized with this [Jira Bug](https://localstack.atlassian.net/browse/LOC-107) by [Unito](https://www.unito.io/learn-more)

authorizerId=authorizer_id)
        self.assertRaises(
            Exception,
            apig.get_authorizer,
            self.TEST_API_GATEWAY_ID,
            authorizer_id
        )
    def test_apigateway_with_lambda_integration(self):
        apigw_client = aws_stack.connect_to_service('apigateway')
        # creat
        lambda_name = 'apigw-lambda-%s' % short_uid()
        self.create_lambda_function(lambda_name)
        lambda_uri = aws_stack.lambda_function_arn(lambda_name)
        target_uri = aws_stack.apigateway_invocations_arn(lambda_uri)
        # creat
        api = apigw_client.create_rest_api(name='test-api', description='')
        api_id = api['id']
        root_res_id = apigw_client.get_resources(restApiId=api_id)['items'][0]['id']
        api_resource = apigw_client.create_resource(restApiId=api_id, parentId=root_res_id, pathPart='test')
        apigw_client.put_method(
            restApiId=api_id,
            resourceId=api_resource['id'],
            httpMethod='GET',
            authorizationType='NONE'
        )
        rs = apigw_client.put_integration(
            restApiId=api_id,
            resourceId=api_resource['id'],
            httpMethod='GET',
            integrationHttpMethod='POST',