Feature flag to disable envar context propagation

[jdcasey]

It should be possible to use an envar (or Quarkus configuration parameter) to disable the envar trace context propagation. In cases where we have other tooling on the system that will use this feature via a sidecar or similar, it would be good to have the flexibility to allow the orchestration system to determine whether the tooling can "own" the parent span ID (in which case trace context would come through a more traditional channel, like http headers).

Specific case: We have a builder image with a sidecar that uses this extension. The builder will normally use envar trace context propagation, as a generic way to tie downstream operations to the orchestration execution that started the builder. However, in some cases, we may use Apache Maven along with its own Opentelemetry extension. When that's the case, we may want the orchestrator to set an additional variable to disable the envar context usage, so the parent spans come from Maven itself, not from the builder that started Maven.