Getting stack output?

**Description:**
To perform automatic integration tests on my project, somehow I need to get the api. There is already the plugin [serverless-stack-output](https://github.com/sbstjn/serverless-stack-output) for Serverless framework that serves the purpose. But I would like to achieve similar thing by AWS SAM after I deploy my application.

Meanwhile, If I can somehow get my api's base url as well as individual endpoints, then I'm able to connect them and and perform tests against them.

**Expected result:**

To get API Gateway endpoints + other invocation channels in a json file.