Returns the current trace ID, if none exists, set the current execution id as the trace id.
This ensures that the client trace id and execution id is the same.
The trace ID remains the same as long as it is in the same process.
Use this method only on the client side.
Returns the current trace ID if it exists, or None if it doesn’t.
This function does not create a new trace ID if one doesn’t exist.
Todo: Eventually use Message Headers to relay this traceid instead of
env vars