[minor request] simplify function templates and enable CORS for local dev

[swyxio]

Is your feature request related to a problem? Please describe.

2 problems:

• users always run straight into CORS issues when they use our default templates. we could help them set CORS headers by default and leave a reminder to tighten it before shipping to prod
• the current DynamoDB CRUD template has a A LOT going on https://github.com/aws-amplify/amplify-cli/blob/7b1f0f2c7bb67a9d154e8462643fb0fe35e88399/packages/amplify-nodejs-function-template-provider/resources/lambda/crud/app.js.ejs and is hard to use. recommend swapping for something simpler like this and pointing to our new guides.

Describe the solution you'd like as above

Describe alternatives you've considered do nothing

[Heldenkrieger01]

What changes need to be made (by hand) in the template right now, to enable CORS?