What does this PR do?

Handle the case where the original handler code returns a side-effect artifact. Such as aws-serverless-express server.

Motivation

https://datadoghq.atlassian.net/browse/SLES-2468

Testing Guidelines

1. Added Unittests
2. Tested with a real lambda application

Additional Notes

Types of Changes

• Bug fix
• New feature
• Breaking change
• Misc (docs, refactoring, dependency upgrade, etc.)

Check all that apply

• This PR's description is comprehensive
• This PR contains breaking changes that are documented in the description
• This PR introduces new APIs or parameters that are documented and unlikely to change in the foreseeable future
• This PR impacts documentation, and it has been updated (or a ticket has been logged)
• This PR's changes are covered by the automated tests
• This PR collects user input/sensitive content into Datadog
• This PR passes the integration tests (ask a Datadog member to run the tests)