feat(aws-lambda): add requestContext field into aws-gateway-compatible input

[windmgc]

Summary

This PR adds a new field requestContext into the lambda input data when the aws-lambda plugin is working in awsgateway_compatible mode.

The requestContext is part of the input data in lambda proxy integration, according to this AWS document page, and it contains many fields containing request related information on AWS API Gateway.

The aws-lambda plugin in Kong provides an AWS API Gateway compatible mode that can generate an input data similar with
the example provided in this doc, but it does not contain the requestContext field. When users are writing their lambda functions with some libraries like aws-serverless-java-container, it will check if the input data have the requestContext field, and if it does not exist, the request will be regarded as malformed.(For example, see this code snippet)

To make the input data sound more "compatible", this PR adds the requestContext field into the input data. Note that many fields in the formal requestContext cannot be fetched by Kong(like IAM-related information or Cognito-related auth info), so we're just providing a best-effort delivery here. We cannot make assurance that the requestContext provided by Kong has every information that the lambda function needs, and it is decided by the lambda function whether the whole payload containing requestContext can work normally or not. So the feature is just a good-to-have one.

Full changelog

• Add requestContext field into awsgateway_compatible input data
• Add related tests

Issue reference

This should fix FTI-2620, and #7641, in some cases.

[Tieske]

why the locals, most are not used, we can add the values in-line to the table below?

(nitpick: feel free to ignore)