feat(event-handler): add first-class support for binary responses

[svozza]

Summary

This PR adds support for base64 encoding of responses. If a handler returns an APIGatewayProxyResult or APIGatewayProxyStructuredResultV2 where the body field is a stream or an ArrayBuffer we will automatically base64 encode it. Handlers can now also just return a stream or ArrayBuffer and we will base64 encode it and set the status code to 200 and the content type to application/json.

Changes

• Handler functions can now return ArrayBuffers and streams, either on their own or as part of a response event, these will automatically be base64 encoded.
• Handler resolution logic detects whether to base64 encode a response and stores decision in the requestContext object in a field called isBase64Encoded. This decision is made by whether the content-encoding header is set ot the the content-type header is image, audio, or video.
• isBase64Encoded field will only be set once, this means that users can over-ride the default detection behaviour by setting base64Encoded in the handler and it will not be changed.
• Added unit tests to test new functionality.

Issue number: closes #4514

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
2.8% Duplication on New Code

See analysis details on SonarQube Cloud

[svozza]

An alternative approach here is to check if we have don't a text-based content type, i.e, if the content type is not one of text/*, application/json, application/xml, application/javascript or application/x-www-form-urlencoded then we base64 encode it. My worry is that there are other non binary types I might be missing here.