Consider using a hidden symbol property on request to stop tracing

[dyladan]

Who removes the header in case http plugin is disabled?

Nobody. If this is important, maybe we should switch to use a hidden property on the request then? Or we could just wait for open-telemetry/opentelemetry-specification#530

I don't really like that we use header values as a signal between plugins. It is an observable side-effect, and quite an intrusive one at that. I much prefer the idea to use context to stop tracing.

Originally posted by @dyladan in #984 (comment)

I really don't like the idea of using header values to signal between plugins, but there is a spec change coming down the pipe that might fix this anyway with a context property that stops tracing.

[pichlermarc]

Closing this as we now have suppressTracing() in @opentelemetry/core which I believe does do exactly this, but via context instead.