Add ability to pass HTTP Headers from AWS Lambda

[Dimitri-Gnidash]

This code adds ability of aws-lambda-status-code to also pass the headers returned by original Lambda functions through Kong Gateway.

This is necessary to support HTTP Redirects that pass additional information for 3XX family of responses in the HTTP Headers.

The expected return array is of the following structure:

{
   "statusCode": 303,
   "headers": {"Location": "https://google.com"},
   "resource": "my value"
}

[Dimitri-Gnidash]

@miaoulafrite @iyp-uk Could you please review this PR? Thank you!