Expose Lambda request ID and trace ID to environment variables

[mnapoli]

Expose these new environment variables on every invocation:

• _X_AMZN_TRACE_ID is a standard AWS Lambda variable that contains the X-Ray trace ID (it is exposed by default on native runtimes)
• LAMBDA_REQUEST_ID now contains the current AWS Lambda request ID

These can then be used in logs to group logs of the same invocation.