[New Community Examples] Examples of idempotent functions

[Nsupyq]

As described in issue #662 , I find that functions under some examples are not idempotent, including aws-node-graphql-api-with-dynamodb, aws-node-express-dynamodb-api, aws-node-mongodb-atlas, aws-python-http-api-with-pynamodb and aws-python-rest-api-with-dynamodb. As suggested in PR #658, I create a new repository. As suggested in PR #662, I suggest that the link should be added into README as a link of community example. Thanks!

[mnapoli]

Hi, feel free to send a pull request to add the examples to the README.

[Nsupyq]

Thanks! I have send a new pull request #669. I find that functions under aws-python-flask-dynamodb-api and aws-python-pynamodb-s3-sigurl are also not idempotent. I will add more examples in my repository.

Please check and close the PR.