Accept X-B3-Sampled header to equal true

[christopher-taormina-zocdoc]

Feature Request

Right now when you use the B3Propagator for the AspNet/AspNetCore instrumentations, the incoming request needs to set the X-B3-Sampled header to 1 for the request to be sampled. As mentioned in the open zipkin repo some tracer implementations may have set this header to the value true instead of 1.

Can the B3Propagator be made to be lenient and accept this value as well? This would put much less burden on anyone moving to the open-telemetry instrumentation when services may have this older implementation.

[reyang]

@vishweshbankwar this looks like a good first issue for you.

[christopher-taormina-zocdoc]

@reyang just opened a PR for this