Wrapper around baggage to propagate.
ThreadLocalAccessor used to propagate baggage via BaggageToPropagate.
ThreadLocalAccessor
BaggageToPropagate
A ThreadLocalAccessor to put and restore current Span depending on whether ObservationThreadLocalAccessor did some work or not (if ObservationThreadLocalAccessor opened a scope, then this class doesn't want to create yet another span).
Span
ObservationThreadLocalAccessor