Add CacheControl headers on the OPTIONS response in AWS API Gateway

[reedyrm]

What did you implement:

Closes #5326

How did you implement it:

Added a conditional check when cacheControl property is present on a cors property for a function, it will add the value as the header for the response. This was only built for AWS API Gateway.

How can we verify it:

I have modified https://github.com/serverless/examples/tree/master/aws-node-simple-http-endpoint example to include the cors change. The cacheControl property is the only new thing that I added.

sample serverless.yml

service: serverless-simple-http-endpoint

frameworkVersion: ">=1.1.0 <2.0.0"

provider:
  name: aws
  runtime: nodejs4.3

functions:
  currentTime:
    handler: handler.endpoint
    events:
      - http:
          path: ping
          method: get
          cors:
            origin: '*'
            allowCredentials: true
            cacheControl: 'max-age=600, s-maxage=600'
            maxAge: 600
            headers:
              - Content-Type
              - X-Amz-Date
              - Authorization
              - X-Api-Key
              - X-Amz-Security-Token
              - X-Amz-User-Agent
              - Cache-Control

Todos:

• Write tests
• Write documentation
• Fix linting errors
• Make sure code coverage hasn't dropped
• Provide verification config / commands / resources
• Enable "Allow edits from maintainers" for this PR
• Update the messages below

Is this ready for review?: YES
Is it a breaking change?: NO

[horike37]

@reedyrm
Thank you for your contribution 👍
Just tested and great to see working fine.

However, you didn't add an explanation of this feature to documentation.
Could you add it around the following section?
https://github.com/serverless/serverless/blob/master/docs/providers/aws/events/apigateway.md#enabling-cors

[reedyrm]

@horike37 Added documentation. Thank you for giving me a link to the documentation, I wasn't sure where it was.

[horike37]

@reedyrm
Thank you for adding it! LGTM 👍