Lambda and Step Functions Span Linking

[kimi-p]

Motivation

To link Lambda span that are triggered by Step Functions with Step Functions span.

https://datadoghq.atlassian.net/browse/SLS-3333

What does this PR do?

This PR sets trace_id and parent_id when Step Functions Context Object is detected in the Lambda handler's event dictionary. The hashing function is implemented as backend and dd-lambda-js.

Testing Guidelines

Tested in sandbox account (trace link).

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)

[kimi-p]

Size is over 86 kb for importing hashlib. Serverless-APM team is planning on reducing the size. It shouldn't be a blocker.

[joeyzhao2018]

LGTM